Takagi Tankless Water Heater Troubleshooting: Complete Guide

If you’re a user of a Takagi heater, no matter what model you use, sooner or later you may find issues. It’s very common especially when you use the heater continuously. In my plumbing career, I’ve already fixed over a hundred Takagi tankless water heater problems. Now, I finally decided to share a detailed Takagi Tankless Water Heater troubleshooting guide with you. 

The common Takagi water heater problems include the heater not turning on, no hot water, the heater not igniting, and others. 

If the heater doesn’t turn on then reset or replace the circuit breaker. When the heater doesn’t heat then replace the heat exchanger or pressure relief valves. Due to ignition failure check the power and gas supply. 

This is just a brief and there are 10+ problems like this. Don’t get frightened, in this article, I’ve discussed everything in proper detail. Just read on and understand how to fix it, 

takagi tankless water heater troubleshooting

Takagi Tankless Water Heater Troubleshooting: 9 General Issues

In the very first segment, I’ll show you the most common Takagi tankless water heater issues with their troubleshooting guide. So, read on. 

ProblemMajor CausesSolutions
Not Turning OnTripped Circuit Breaker, Faulty Breaker, Faulty WiringReset circuit breaker, Replace faulty breaker
No Hot Water/Not HeatingWrong Power Supply, Gas/Water Valve Issues, Dirty FilterCheck power supply and valves, Clean filter
LeakingCorrosion, Faulty Pressure Relief Valve, Bad Water ConditionsReplace the heat exchanger, Replace the pressure relief valve
Water Too HotReplace the heat exchanger, Replace the pressure relief valveAdjust temperature setting, Check/replace sensor
Temperature FluctuationsImproper Installation, Plumbing Issues, Gas Supply IssuesReview installation, Fix plumbing or gas supply
Unit Not IgnitingNo Power, Gas Supply Turned Off, Low Flow RateCheck power and gas supply and ensure minimum flow rate
Fan Motor Keeps SpinningNormal Operation After ShutdownAllow the fan motor to complete its cycle
Abnormal SoundsDebris Accumulation Inside FanManually clean the fan
Remote Control IssueNo Power Supply or Connection IssuesVerify power supply, Check and correct connections

Problem 1: Takagi Tankless Water Heater Not Turning On 

A common problem I found while troubleshooting the water heater is – the Takagi tankless heater not turning on. Below I’m showing the troubleshooting guide for this. 

i) Tripped Circuit Breaker: Somehow if the circuit breaker of the water heater trips, it’ll cut the power as it acts as the safety switch. So, due to the lack of electricity, there will be no power and the heater won’t turn on. 

Solution: To fix this, locate the electrical panel or breaker box in your home and check if the circuit breaker is tripped. If so, reset the breaker. If damaged, replace the circuit breaker.

ii) Turned-Off Breakers: It can be also possible that someone intentionally turns off the breakers for repair or other reasons and forgets to turn them back on.  In that case, the water heater will have no power supply. As a result, the heater won’t receive electricity and won’t turn on. 

Solution: It’s no big deal to repair it. Just inspect the breakers to see if any are in the “off” position. If you find it off then switch them to the “on” position to restore power.

iii) Faulty Breaker: Due to long-time use or for other reasons the breaker can get faulty. If it’s faulty, it won’t let electricity pass to the heater and the heater won’t turn on. 

Solution: To fix this, identify the faulty breaker and replace it. If you aren’t a professional consult a qualified electrician to safely replace it.

iv) Faulty Wiring: If the water heater doesn’t turn on even if there is a proper connection the reason can be faulty wiring. This can happen during installation, especially if the electrician is inexperienced.

Solution: To solve the issue, contact a licensed electrician or a technician experienced in water heater installations and fix the wiring.

v) Closed Shut-Off Valve: If the shut-off valve of the water inlet source is closed or not fully open, it can restrict water flow to the unit. And your heater needs a minimum water flow of 0.5 gallons per minute to turn on. So, due to a closed shut-off valve, your Takagi tankless heater won’t turn on.

Solution: To solve this, locate the shut-off valve on the water inlet source and ensure that it is fully open. After opening the shut-off valve, check if the water heater now turns on.

vi) Low Water Supply Rate: Tankless water heaters require at least 0.5 GPM water flow to activate. If the water supply is lower than that, the heater will not turn on. 

Solution: You need to ensure the water flow rate is a minimum of 0.5 GPM. To do so you can test the water supply rate in your home. You can also consider options such as cleaning clogs, upgrading plumbing, or consulting a professional for a suitable solution.

vii) Dirty Filter Screen: If the inlet side filter screen is dirty and clogged, water can’t flow through it properly. As a consequence, the required amount of water can’t go through the heater to turn it on. 

Solution: To fix this, turn off the power and water supply, clean the filter screen, and ensure proper reassembly. If you need a detailed guide on cleaning then check the linked article. 

Problem 2: Takagi Tankless Water Heater No Hot Water/Not Heating

The next Takagi gas water heater problem users generally face is the heater not heating and no hot water. There are mainly 4 situations when you can face this problem. Let’s get to know a bit about them. 

Condition 1: No Hot Water When A Fixture Is Opened

Sometimes you may find no hot water when a fixture is opened. The possible causes for this issue are wrong power supply, partially opened gas/water supply valve, lack of gas, or dirty filter.

How To Fix It?

To fix this issue follow the below procedure. 

  1. Make sure the heater is running with the right power supply. Check the power supply rating(120 VAC, 60 Hz).
  2. Check the remote or temperature controller settings and make sure it’s turned on.
  3. Ensure gas and water supply valves are fully open.
  4. Clean the filter on the cold water inlet.
  5. Make sure there is enough flow rate (0.5 GPM).
  6. Address freezing issues in cold areas.
  7. Verify correct setup for Easy Link or Multi-Unit systems.
  8. Check for reverse plumbing, especially in 140 Indoor and 140 Outdoor models.

Condition 2: Not Enough Hot Water

Sometimes, the heater produces hot water but the water isn’t not enough. This problem can occur due to plumbing issues, partially opened/closed gas supply valves, inadequate gas pressure, incorrect POU mixing valve adjustments, and hard water scaling.

How To Fix It?

Below you’ll get a quick guide on fixing the issues. 

  1. First, make sure to have proper water flow and temperature settings.
  2. Next, check for cross-connections, and if found fix the issue.
  3. Make sure to open the gas supply valve fully and check gas line sizing and pressure.
  4. Check for correct POU mixing valve adjustments.
  5. Check for hard water scaling and get rid of it through the descaling process.
  6. If you find the 101 error code then take action accordingly following the user manual.
  7. Finally, if the airflow is blocked then clean vents, burner, and heat exchanger for optimal airflow.

Condition 3: Takes Too Long To Get Hot Water

It’s really disgusting when you find the water taking too long to produce hot water. There are several reasons behind this. First, long-distance or large pipes between the heater and faucets. Second, lack of a recirculation system, and third insufficient insulation can occur.

How To Fix It?

Fixing this issue is not very tough. Let’s see how you can fix them. 

  1. Install a recirculation system to keep hot water moving through pipes.
  2. Insulate hot water pipes to reduce heat loss. To do it just wrap up the pipes with insulation material.
  3. Regularly clean filters in the water system to improve water flow.

Condition 4: Hot Water Turns Cold And Stays Cold

The final condition is when hot water turns cold and remains cold. There are several reasons for this issue such as Insufficient water flow, lack of check valves in the recirculation system, gas valves not fully open, dirty cold water filter, and blocked faucets/shower heads.

How To Fix It?

Now let’s get the procedure to fix the issues. 

  1. First, you’ll have to ensure smooth water flow through the heater.
  2. Use an adequate number of check valves in recirculation systems.
  3. Ensure that the gas valve is fully open.
  4. Clean the filter where cold water enters.
  5. Inspect and clean blocked faucets and showerheads.

Problem 3: Takagi Tankless Water Heater Leaking

Another major issue with the Takagi tankless water heater is that the heater is leaking. It generally occurs in the old water heater. Let’s see how to troubleshoot this. 

i) Damage/Corrosion: The primary cause of leaks in a Takagi tankless water heater is damage or corrosion in the heat exchanger. First, it can occur due to contamination issues.  If the air around the water heater contains dust, sand, lint, grease, or other impurities, these can enter the heater and accumulate in the fan and burner parts. As a result, the heat exchanger gets damaged.

Again due to limescale buildup, it can happen. When the water has high hardness (above 7 grains or 70‐140 ppm), it leaves limescale inside the pipes. As a result, the copper pipes inside the heater can get damaged which eventually damages the heat exchanger. 

Solution: I would recommend only one solution to solve the issue, replace the faulty heat exchanger and carefully reassemble it. 

ii) Faulty Pressure Relief Valve (PRV): The pressure relief valve releases extra pressure from the water heater. If it’s broken or installed incorrectly, it can leak water.

Solution: To solve this you’ll have to replace the faulty pressure relief valve with the right size and pressure rating. It’s best to get help from a professional plumber for this.

iii) Bad Water Conditions (Hard or Acidic Water): Hard water with lots of minerals or acidic water can damage the tankless water heater and cause water leakage.

Solution: For hard water, use a water softener and for acidic water, try a neutralizing filter or chemical treatment. One tip for you; regularly flush the system to remove built-up minerals.

iv) Improper Venting: If the venting system is not set up right or is blocked, it can cause problems with the water heater and lead to leaks.

Solution: Make sure the venting is correct and clear. If not then consult a professional and set it up again.

v) Condensation Issues: During winter, tankless water heaters can create condensation. If the drain line is not installed properly or is clogged, it may cause leaks.

Solution: Check the drain line for clogs and proper installation. Clear any blockages and ensure the drain line has a proper slope.

vi) Loose Connections: Over time, vibrations and changes in temperature can loosen connections and cause water leaking.

Solution: To fix loose connection issues, tighten loose connections, fittings, or joints. Use thread seal tape or pipe joint compound for a secure seal.

vii) Corrosion: Corrosion, especially in areas with hard water, can weaken the water heater structure and cause leaks.

Solution: Here the solution is to replace corroded components, like the heat exchanger. Consider a water softener to prevent hard water effects. 

vii) Temperature and Pressure Fluctuations: Quick changes in temperature or high water pressure can stress the water heater and cause water leaks.

Solution: Install a pressure regulator to keep water pressure in the recommended range. 

viii) Improper Installation: Sometimes, mistakes in installation, like wrong gas line size or venting issues, can lead to leaks.

Solution: Follow the manufacturer’s guidelines for installation. Fix any venting, gas line, or clearance issues. 

ix) Freezing Conditions: Your water heater needs to be protected against freezing, If not, cold weather can cause the tankless water heater or pipes to freeze which causes leakage.

Solution: Insulate pipes or use freeze-protection devices to prevent freezing.

Problem 4: The Water Is Too Hot

Sometimes you may find the water too hot which can burn the skin. This is another common issue and below check the troubleshooting guide. 

i) Too High-Temperature Setting: By any chance, if you set the temperature rating too high then the heater will produce too hot water.

Solution: Use the DIP Switches on the PCB or the remote controller to lower the temperature.

ii) Issues with the Temperature Sensor: The temperature sensor may not be working correctly, affecting temperature readings.

Solution: Check the sensor by following the instructions in the Maintenance Sheet (usually behind the front panel). Turn off the power, run cold water through it, and ensure the temperatures match on the remote controller.

Problem 5: Temperature Fluctuates When A Fixture Is Opened

The fifth problem isn’t always common but while troubleshooting the Takagi water heater, I faced it sometimes. Let’s see the way to fix this. 

i) Improper Installation: If the units aren’t installed properly it can occur. 

Solution: Review the installation instructions and make any necessary adjustments to ensure proper installation.

ii) Plumbing Line Issues: Plumbing line issues such as cross plumbing between cold and hot water lines, or issues with a check valve installation can cause the problem

Solution: First fx cross plumbing issues. Next, inspect the check valves for proper operation and install or fix them as needed.

iii) Recirculation System Problems: If there are issues with the recirculation system such as issues with check valves, air cavitation, pump operation, or directional indicator, this problem can occur

Solution: Make sure the check valves are okay and check if the pump is working right. Fix any air bubbles, check which way the pump is pointing, and make sure the pump is big enough (at least 2 gallons per minute)

iv) Gas Supply Issues: If the gas supply lines aren’t sized correctly, the propane tank level is lower, or if there is an issue with the gas supply pressure regulator then this issue can occur. 

Solution: To fix this issue, first, resize gas supply lines if needed. Next, refill propane tanks for LP models, and fix any issues with the gas supply pressure regulator.

v) Venting Problems: If the exhaust venting isn’t installed properly or the vent run exceeds the maximum limit (50 ft.), a temperature fluctuation problem may occur. 

Solution: To fix this issue, Install the exhaust venting properly. Next, ensure that the venting meets the manufacturer’s specifications and adjust if necessary to stay within the maximum limit.

vi) Water Pressure Fluctuations: If there are fluctuations in water pressure, especially on low flow, it can lead to temperature fluctuation.

Solution: Adjust the system or consult with the Technical Department for guidance.

vii) Compromised Flow Sensor or Water Control Valve: If the flow sensor or water control valve is compromised, you can face this issue. 

Solution: Consult any certified technician to fix issues with the flow sensor or water control valve.

viii) Dirty Cold Water Inlet Filter: If the cold water u-inlet filter is dirty it can cause water temperature fluctuation issues. You can also look for signs of hard water scaling

Solution: Properly clean the cold water inlet filter and it’ll be fixed. 

Problem 6: The Unit Doesn’t Ignite When Water Goes Through It

This ignition issue is also very common and there are 7 reasons behind this. Let’s get the issues and solutions.

i) No Power to Water Heater: Is the power of the heater turned on? The water heater won’t ignite if the power is switched off

Solution: Check and ensure that the power to the water heater is turned on.

ii) Gas Supply Turned Off: If the gas supply is turned off, the water heater won’t ignite.

Solution: To fix it, just check and turn on the gas supply.

iv) Low Flow Rate Issue: Your heater won’t ignite if the water flow rate is below 0.5 GPM (1.9 L/min).

Solution: To ensure ignition, increase the flow rate to at least 0.5 GPM 

v) Dirty Cold Water Inlet Filter: Is the cold water inlet filter dirty? A dirty cold water inlet filter can also prevent ignition.

Solution: Clean the cold water inlet filter following the user manual. 

vi) Reverse or Cross Connection Problem: Another reason for Ignition issues is reverse or cross connection.

Solution: Contact any certified plumber and fix issues related to reverse or cross-connection.

vii) Inlet Temperature Too Close to Set Temperature: Ignition can also occur if the inlet temperature is too close to the set temperature.

Solution: Adjust the inlet temperature to a level significantly different from the set temperature. It’ll allow proper water heater activation and solve the issue. 

Problem 7: Fan Motor Keeps Spinning After The Operation Has Stopped

This is another rare problem I’ve faced a few times. You may sometimes notice the fan motor continues to spin for 5 to 50 seconds after the operation stops. It does this to quickly restart and get rid of the old air from the pipe where the smoke goes out

How To Fix It?

No need to be worried about this issue, This is a normal operation and you don’t have to take any action to fix this. It ensures efficient performance and safety. So, allow the fan motor to complete its post-operation cycle.

Problem 8: Abnormal Sounds Come From The Unit

Sometimes you may notice the Takagi tankless water heater making noise and it’s coming from the unit. It generally occurs when debris accumulates inside the fan. 

How To Fix It?

The first thing you can try is to manually clean the fan and get rid of the debris. If it doesn’t work then consult any technician for further help. 

Problem 9: The Remote Control Doesn’t Display Anything

This is not directly related to the Takagi water heater problem. Instead, it’s an issue related to the remote control. Sometimes the remote controller does not show any information when the power button is turned on. Let’s see the reasons and solutions here. 

i) Normal Operation: This might not be a problem instead this is normal behavior. The display turns off to conserve energy when the unit has not operated for five minutes or more. So, there is no need to fix this issue. This is a part of the unit’s energy-saving feature.

ii) No Display (Lamp Does Not Light Up): If there is no power supply to the unit or there is a problem with the connection to the unit the remote won’t display anything. 

Solution: First, verify the unit has a stable power supply. Next, check and correct the connection to the unit to enable proper functionality.

Model-Wise Troubleshooting Guide For Takagi Tankless Water Heater  

Till now I’ve explained 9 common problems of Takagi tankless water heaters. No matter which models you use you can face the issues. But now I’ll mention some problems that users of specific models usually face. Let’s check them out.

Troubleshooting Takagi T-KJr, T-H3, T-K4, T-D2 Water Heaters

If you’re a user of the following model you may face 2 specific problems. Let’s get a troubleshooting guide for them.

All Sinks Lose Water Pressure When The Dishwasher Is Filling Up

This incident is very common and frustrating. If you are a user of one of the following models there is a chance of facing this. Let’s see the reasons for this issue and how to troubleshoot this. 

i) Mismatched Heater Capacity and Dishwasher Demand: If the heater’s capacity doesn’t match the gallons per minute (GPM) demand of the dishwasher it can occur. 

Solution: Verify and ensure that the heater can meet the GPM demand of the dishwasher.

ii) Inadequate Dishwasher Supply Line Size: If the size of the supply lines to the dishwasher is insufficient you may face this issue. 

Solution: Check and, if necessary, upgrade the size of the supply lines to meet the dishwasher’s requirements.

iii) Water Regulator Setting on Dishwasher: Is the water regulator on the dishwasher set incorrectly? If so, then there is a chance of facing this problem. 

Solution: To fix this, ensure the recommended supply water pressure on the dishwasher’s rating plate and adjust the water regulator accordingly.

iv) Hard Water Scaling in the Unit: If there is hard water scaling in the unit then it can reduce water pressure and flow.

Solution: Regularly check for and address hard water scaling to maintain proper water pressure and flow. If required, consider adding a water softener.

Unit Doesn’t Turn On Despite Having Power, Gas, And Water

Sometimes a rare problem occurs when there is a required gas and power but the unit doesn’t turn on. Let’s see how to fix this.  

i) Incorrect Plumbing Installation: In most cases, if the unit is plumbed in backward this problem can occur. 

Solution: To fix this follow these steps:

  1. Turn off the cold water feed only.
  2. Open the nearest hot water tap and ensure that the water flow stops. If it continues, there may be a cross-connection with cold water. So, fix the cross-connection issue.
  3. Open the pressure relief valve and confirm that the water flow stops. If it doesn’t, it indicates that the unit is plumbed backward. In that case, you’ve to replumb the unit in the correct orientation. 

ii) Clogged Filter: Another issue for this problem is the filter is dirty.

Solution: Here the solution is very easy. Just clean the filter as per the instructions.

iii) Faulty Water Flow Sensor: If there is an issue with the water flow sensor then the problem can also occur.

Solution: Check and clean the water flow sensor to ensure proper functioning. If the issue persists, consult with the technical support for further assistance.

If you’re still confused about your model, I’m mentioning the models more specifically 

  • 240 (Indoor/Outdoor)
  • 340 (Indoor/Outdoor) 
  • 540 (Indoor/Outdoor)
  • 110 (Indoor/Outdoor)
  • 310 (Indoor/Outdoor)
  • 510 (Indoor/Outdoor)

Takagi Tk3 And TK3 Pro Troubleshooting

There are a lot of users of the Takagi T-K3 and T-K3-Pro water heaters. Now the users of these models usually face 3 common problems that are less seen in the other models. They are; 

  1. The heater takes too long to produce hot water
  2. Hot water turns cold and stays cold 
  3. Hot water is unavailable when a fixture is opened

In the general troubleshooting guide under Problem 2, I’ve explained all the 3 problems with their troubleshooting guide. If you want to learn more check the linked section. 

Takagi TK1S And Tk2 Troubleshooting

The users of Takagi T-K1S and T-K2 may face one unique issue: the heater won’t initiate. Let’s see the reasons and solutions for this Takagi tankless TK1S  and T-K2 heater.

Takagi T-K1S/T-K2 Will Not Initiate

There are mainly 2 reasons for this initiating issue of the T-K1S/T-K2 water heater. Let’s get the issues and solutions. 

i) Insufficient Flow Rate: The most common reason behind this problem is insufficient flow rate. If the flow rate through the unit is below 0.75 GPM the heater won’t initiate. 

Solution: To solve this, just ensure the flow rate is at least 0.75 GPM. Also, check the filter and flow sensor for debris or damage.

ii) Electrical Supply Issue: If there is an issue with the electric supply this issue can occur. The red light above the lower green button on the GFCI won’t come on then.

Solution: To fix this, first, check the electrical supply to the unit. If the red light is off, press the green reset button above it. Verify the green light on the circuit plate at the top left of the unit is lit. If not, there might be an issue with the electrical connection between the GFCI and the circuit plate. Contact any certified electrician to fix this. 

Takagi Tankless Water Heater Error Code

Aside from general issues, your other neck in pain can be the Takagi tankless water heater error codes. Very often you may notice error codes displaying on the water heater. 

Error CodeDescriptionTroubleshooting Steps
031Incorrect DIP Switch settingsTurn off the power, and check and adjust the dip switch settings.
101Abnormal combustionCheck the airway, and manifold pressure, clean burner, and adjust altitude dip switches.
111Ignition failureCheck the hi-limit switch, gas supply, pressure, clear plastic tube, and flame sensor.
121Flame lossFollow the same procedure as the previous one
311, 321, 331Thermistor issuesCheck wire connections, and resistance value, clean, and replace thermistor if needed.
391Air-Fuel Ratio Rod FailureCheck wire connections, clear plastic tubes, and clean AFR.
441Flow sensorVerify water supply, check wire connections, and clean flow sensors.
510, 55Abnormal gas valvesTurn off the gas and power if the flames persist. Check wire connections and gas pressure.
611Abnormal fan motorTurn the power off and check the wiring and fan housing for water. Replace PCB if needed.
651Flow adjustment valveTurn off power, check wire connections, inspect for leakage, and clean or replace the valve.
701Computer board faultCheck wire connections, inspect PCB, verify gas pressure and contact support.
721False flame detectionShut off gas and power, and contact support.
741Remote control problemCheck the wiring and remote model. Ensure a single remote and avoid disconnecting with power on.
761Communication failureVerify power, check communication cable setup, and look for power surges.
991Abnormal combustionFollow the procedures for error code 101, and contact support if the issue persists.

Error Code 031: Incorrect Dip Switch Settings

If you encounter Error Code 031, start by turning off the power supply. Next, check the dip switch settings on the computer board. Follow the user manual and adjust the switches to the correct dip switch positions. Finally, ensure the gas type dip switch is correctly set, and reset the computer board if the issue is resolved.

Error Code 101: Abnormal Combustion

Error Code 101 generally indicates abnormal combustion. To fix this you’ll have to follow a systematic approach. First, check for airway blockages, verify manifold pressure, clean the burner in case of contaminated intake air, address weather-related issues, and adjust dip switches for high altitude if needed. Now, confirm that all dip switches are set correctly and reset the computer board after the issue is fixed.

Error Code 111: Ignition Failure

For Error Code 111, which occurs due to ignition failure, take several steps. Start by verifying that the hi-limit switch is not tripped and check both the gas supply and pressure. Inspect the clear plastic tube connected to the gas valve, check the overheat cutoff fuse, and clean the flame sensor. Finally, ensure that the igniter produces a spark and inspect for any venting blockages.

Error Code 121: Flame Loss

Error Code 121 indicates flame loss during operation. The troubleshooting procedure for error code 121 and error code 101 is almost the same. So, first, make sure that the hi-limit switch is not tripped, check the gas supply and pressure, inspect the clear plastic tube connected to the gas valve, and clean the flame sensor. Additionally, check for blockages in the venting system and inspect the PC Board for potential faults.

Error Code 311: Output Thermistor

If you encounter Error Code 311 related to the output thermistor, start by checking wire connections and the resistance value. Clean the thermistor and if the issue persists, consider replacing the thermistor.

Error Code 321: Inlet Thermistor

Error Code 321 indicates issues with the inlet thermistor. To fix this error code follow the previous troubleshooting steps for error code 321.

Error Code 331: Mixing Thermistor

The issue with the mixing thermistor persists for Error Code 331. Here again, the procedure is the same as the Error Code 311.

Error Code 391: Air-Fuel Ratio Rod Failure

Due to air-fuel ratio rod failure, you’ll see Error Code 391. To solve this, first, check the wire connections and the clear plastic tube. Next, clean the air-fuel ratio rod and it should be fixed.

Error Code 441: Flow Sensor

Error Code 441 occurs due to issues with the flow sensor. To get rid of this error code, confirm the proper water supply, check wire connections, inspect the inlet filter, and check the flow sensor for any debris.

Error Code 510: Abnormal Gas Valves

Due to an abnormal gas valve Error Code 510 appears and it requires immediate attention. If the hot water is off but flames are visible, shut off the gas and power. Also, check wire connections, verify proper gas valve wiring, and confirm the supply gas pressure is within specified limits.

Error Code 55: Abnormal Solenoid Gas Valve

Error Code 55 indicates an abnormal solenoid gas valve. Follow the same steps as error code 510 to get rid of this.

Error Code 611: Abnormal Fan Motor

Due to an abnormal fan motor Error Code 611 will be displayed. To fix this, turn off the power supply and inspect the fan motor wiring. Check the fan housing for water, and if the issue persists, consider replacing the PCB.

Error Code 651: Abnormal Flow Adjustment Valve

Error Code 651 indicates issues with the flow adjustment valve. To get rid of this, turn off the power supply, check wire connections, inspect for water leakage, and clean or replace the valve. Additionally, inspect the PCB for potential faults.

Error Code 701: Computer Board Fault

When the Error Code 701 appears, it indicates a computer board fault. To solve this, turn off the power supply and inspect wire connections. Examine the PCB for any signs of damage or faults. Next, verify the supply gas pressure, and if you aren’t able to fix this, contact professionals.

Error Code 721: False Flame Detection

Error Code 721 indicates false flame detection and requires immediate action. Immediately shut off gas and power, and contact any certified technician for further assistance.

Error Code 741: Main Remote Control Problem

Due to the main remote control problem Error Code 741 appears. To fix this error code, first, check the wiring to the remote and verify the correct remote model. Then ensure only one remote is installed, and turn off the power before disconnecting the remote. Additionally, check for any signs of power surges.

Error Code 761: Communication Failure

Error Code 761 occurs due to communication failure in a multiple heater setup and the code only appears on the master heater. First, confirm there is power to the unit that lost communication. Then follow the manual, set up the communication cable properly, and look for any signs of power surges.

Error Code 991: Abnormal Combustion

Just like error code 101, error code 991 appears due to abnormal combustion. To fix this follow the same troubleshooting steps for Error Code 101. If the issue persists, contact the Technical Service Department. Finally, when the problem is resolved, adjust the manifold gas pressure.

How To Reset Takagi Tankless Water Heater? Step-by-Step Guide 

To troubleshoot the Takagi water heater, resetting it is a common procedure. In this segment, I’ll show you how to reset the Takagi tankless water heater. 

Step 1: Ensure Water Flow Is Stopped

Before you start, ensure that water is not flowing through the Takagi Tankless Water Heater. This precautionary step is essential to prevent potential hazards during the reset.

Step 2: Turn Off The Temperature Remote Controller

If your water heater comes with a temperature remote controller then turn off the remote controller. It’ll ensure that the unit won’t receive any commands during the reset process.

Step 3: Power Off The Tankless Unit

Now. Locate the power switch on the Takagi Tankless Water Heater and switch it off. Wait for a few seconds, and then turn the power back on.

Step 4: Remove The Front Access Panel

Once you’ve confirmed the water heater is safe to work with, access the reset button by removing the front access panel. Use a screwdriver or an adjustable wrench to carefully take off the panel.

Step 5: Locate Reset Buttons

After removing the front access panel, locate the computer board inside. Look for two reset buttons labeled “INC” and “DEC” on the computer board. These buttons are integral to the reset process.

However, the reset button location is different for different Takagi models. 

For the HX3, H3, T-H3S, T-H3j, CX3, Ct-199, and 540 series, you’ll find the reset button on the computer board in the following arrangement.

computer board of takagi tankless water heater

Now, for T‐KJr2, T‐K4, and T‐D2 models, you’ll get the reset button in the following arrangement 

locate the T‐KJr2, T‐K4, and T‐D2 models of takagi tankless water heater

Step 6: Press And Hold the Buttons

Now, simultaneously press and hold both the “INC” and “DEC” buttons on the computer board for a few seconds. Continue holding them until a red LED light illuminates, It’ll indicate that the reset process is in progress.

Step 7: Release Buttons And Power Off Unit

Once the red LED light appears, release both the “INC” and “DEC” buttons. Now, turn off the Takagi Tankless Water Heater using the power switch.

Step 8: Power On The Water Heater

This is the final step. When the unit is turned off, wait for a moment, and then turn the water heater on. You should observe that the water heater has been successfully reset. The unit is now ready for normal operation.

Takagi Tankless Water Heater Maintenance

I’ve already discussed all the Takagi gas and electric water heater troubleshooting guides. And I think you won’t be wanting to get the issues back. If you don’t want to then you’ll have to follow some maintenance guide. 

Takagi water heater maintenance is a broad fact that can’t be discussed properly in short. I’ve already prepared an article on the maintenance guide for the Takagi water heater. So, if you’re interested then check the linked article.

However, here I’m shortly addressing the major maintenance task with a step-by-step guide. 

Cleaning The Combustion Components

The combustion components include the burner, flame sensor, fan, and Air-Fuel Ratio (AFR).

  1. To clean the combustion components, start by disconnecting the power and gas supply.
  2. Now, remove the front cover, then disassemble the manifold plate and gas valve assembly. 
  3. After that Carefully detach the burner assembly, and clean it using a degreaser.
  4. Don’t forget to clean the fan by covering the fan port and blowing compressed air. 
  5. Now, inspect the combustion chamber with a flashlight and clean it using a shop vacuum and air compressor. 
  6. Finally, clean the sensors using sandpaper, reassemble the unit, and ensure all gaskets are intact.

Cleaning The Rod Assembly

Another major maintenance is cleaning the rod assembly. Let’s see how to do it.

  1. Start by removing the front cover and locating the rod assembly. 
  2. Gently clean the flame sensor and air-fuel ratio rod using 100-grit sandpaper. 
  3. After that reassemble the rod assembly and ensure the sight glass, rods, and gasket are in their original positions.
  4. In the last step, reattach the front cover and wires and double-check all connections.

Cleaning The Filter

Cleaning the filter is even necessary for troubleshooting many issues. Let’s get the steps to do it. 

  1. For this maintenance task, first, adjust the water heater temperature, heat the water, and then turn off the power.
  2. Now, isolate the water heater, prepare a vinegar solution, and connect the hoses to a submersible transfer pump.
  3. Run the pump for 45 minutes to clean the system. Drain the vinegar, flush with water, and repeat the drainage steps.
  4. Finally, reopen the isolation valves, allowing the system to operate at the previous temperature.

Unit Draining & Power Outage (Freeze Protection)

When you’re planning not to use the heater for a while, this maintenance is necessary. This helps prevent the water heater from freezing and getting damaged. Let’s see how to do it. 

  1. First, close the manual gas shutoff valve and turn off the power.
  2. Now, close the inlet water valve, and open all hot water taps. 
  3. After that Drain the unit, including the X3™ Cartridge, and ensure all water is removed.
  4. Keep valves closed and power disconnected. Securely screw the drain plugs back in place.

Descaling The Unit

Continuous use of your water heater may accumulate hard water deposits to the heat exchanger. Descaling is necessary to remove hard water deposits and maintain optimal water heater performance. It also helps to increase the lifespan of the water heater. Let’s learn about the descaling process in short. 

descaling process of takagi tankless water heater
  1. First, adjust the temperature and set it to 140°F using the remote controller. 
  2. Now open any hot water fixture and let the heater operate for 60 seconds. 
  3. Now turn off the power and close the isolation valves (C & D) to isolate the water heater.
  4. Now, prepare a vinegar solution, and connect hoses to a submersible transfer pump.
  5. After that run the pump for 45 minutes, drain the vinegar, and flush with water.
  6. Repeat drainage steps, open valves, and turn on the power.
  7. Finally, adjust the temperature and remove any remaining air from the water line.

How To Adjust Takagi Water Heater Temperature?

Adjusting the temperature of your Takagi Tankless Water Heater is a simple process. Here’s a step-by-step guide that covers most models

Step 1: Power On The Unit

Before you start the process, ensure that the Takagi tankless water heater is connected to a 120 VAC power supply. This ensures the unit is ready to be adjusted.

Step 2: Turn On The Controller

Now press the “ON/OFF” button on the controller to turn it on. When the controller is turned on, the STAND BY LED light will indicate that the unit is in standby mode and ready for adjustments.

Step 3: Set The Desired Temperature

Now the controller is showing the current temperature setting. Let’s see how you can adjust this setting to your desired temperature:

  • To increase the temperature press the “HOT” button 
  • To decrease the temperature, press the “COLD” button.

Increasing Temperature Beyond 120 °F (50 °C)

If you want to set the temperature higher than 120 °F (50 °C) then follow the below steps. 

  1. Ensure the water heater is in stand-by mode.
  2. Press the “HOT” button, setting it to 120 °F (50 °C).
  3. Press and hold the “INFO” button and the “HOT” button for at least 3 seconds. The controller will beep and change to 125 °F (52 °C).
  4. Press the “HOT” button to set the temperature up to 140 °F (60 °C).

Increasing Temperature Above 140 °F (60 °C): For 540HX3/510CX3 Model

If you have the 540HX3/510CX3 model and need to increase the temperature above 140 °F (60 °C), follow these steps:

  1. First, ensure that the heater is in StandBy mode.
  2. Now, press the “HOT” button, setting it to 140 °F (60 °C).
  3. Hold down the “INFO” and “HOT” buttons for at least 3 seconds. The controller will beep and switch to 145 °F (63 °C).
  4. Press the “HOT” button to increase the temperature to a maximum of 160 °F (70 °C).

This is the simplest way to change the water heater temperature. Aside from that, there is another way to change it and it’s by using the DIP Switch settings. Again, the process I’ve mentioned won’t apply to all the Takagi water heater models. For example, the process is slightly different for the 910/910 ASME models. To learn more about the temperature adjustment procedure of the Takagi Tankless water heater, visit the linked article. 

Takagi Water Heater DIP Switch Settings

DIP switch settings in a Takagi Tankless Water Heater comprise various configurations, each serving different purposes and functions like choosing the type of gas, how fast the fan spins, and even dealing with really cold temperatures. It’s highly important to get these settings right so that the heater works just the way it’s supposed to.

The DIP Switch settings for different Takagi models are different. However, below I’m mentioning the setting for 2 common models; 240HX3 and 340HX3. 

SettingDIP Switch Number240HX3/340HX3 Models
Gas Type Selection1 and 2Propane: ON, OFF
Fan Motor Speed Control3, 4, 5Default: OFF, OFF
High-Altitude Installation (240HX3/340HX3)3, 4, 5Default, 0-2,000 ft
High-Altitude Installation (540HX3)2, 3, 4Default, 0-2,000 ft
Vent Length (Two-Pipe, Direct-Vent)3, 4Default: 5-20 ft
Vent Length (Single Pipe with Room-Air)3, 4Default: 5-45 ft
Temperature Adjustment (910/910 ASME)1, 2, 38 Levels (See guide)
Temperature Adjustment (240HX3/340HX3)9120 °F (50 °C)
Temperature Adjustment (540HX3/510CX3 and 540P)5120 °F (50 °C)
Exhaust Temperature Control10 (6 for 540)Default: OFF


What is the most common issue with tankless water heaters?

The most common issues with the Takagi tankless water heaters are the water takes too long to provide hot water and the heater isn’t heating. 

What is Takagi Tankless Water Heater Standby?

When the Takagi water heater is in standby mode, it means it’s turned on but not actively operating. In standby, the heater actually remains idle and the purpose of this mode is to save energy.

What is the code 111 on Takagi?

Due to ignition failure Error Code 11 appears. To solve this check the hi-limit switch and ensure proper gas supply pressure. Additionally, clean the flame sensor and remove any blockages in the venting.

What is the warranty on a Takagi water heater?

The warranty for a Takagi water heater depends on its application. For residential use, you’ll get a warranty of 15 years for the heat exchanger but for all other parts (excluding fuses), you’ll get a warranty of 5 years. In commercial settings, the warranty for the heat exchanger is 10 years, and the warranty for the other parts is 5 years.

Final Verdict

This is the last segment of this article. In this guide, I’ve discussed everything related to Takagi Tankless Water Heater troubleshooting. First I’ve mentioned the usual problems with their troubleshooting guide. Then I’ve discussed the model-based specific problems. So, no matter which model of Takagi heater you use, you’ll get the solution to your problem. 

Now it’s time to end the article. However, before I finish I must encourage you to read the maintenance part again and act accordingly to prevent regular problems and increase the lifespan of the heater. One more thing, if you’re not a professional don’t try to fix the complex issues manually. You better consult any certified technician or Takagi tankless water heater customer service (888.882. 5244)

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