Takagi Tankless Water Heater Error Code 101[Fixed]

Takagi tankless water heaters offer energy-efficient and continuous hot water on demand. However, like any appliance, they can also encounter issues that require troubleshooting one common way they communicate problems is through error codes.

So, what does Takagi tankless water heater error code 101 mean?

The code 101 is actually a head-up or warning for the code 991. This code means it’s having imperfect combustion that needs to be addressed. If not addressed, the heater will show code 991 and stop working. 

From my years of experience with troubleshooting Takagi tankless heaters, these are the common fixes for this code. 

  • Ensure proper gas type
  • Make sure there’s no blockage in the inlet or outlet air
  • Ensure the distance between terminals is proper
  • Ensure the heater is installed within the appropriate altitude range and DIP switches are adjusted correctly. 

To know how to make sure of all these factors, you have to read the full article. 

takagi tankless water heater error code 101

Takagi Tankless Water Heater Error Code 101- What Does It Mean?

The error code 101 in the Takagi tankless water heater tells you that there’s a problem with the mixture of air and fuel being used for combustion. It’s too rich in gas, which is bad for the heater. This can happen if the gas lines that supply the fuel are too small.

Initially, when this situation of imperfect combustion arises in the water heater, the heater will continue to work but will show error code 101 in the controller. Along with that, you will see five green flashes in the LED monitor. 

If you don’t fix the problem even after seeing this code, the heater will eventually shut down on its own. After that, you will see an error code 991 in the controller, and the heater won’t work. So basically, the error code 101 in the Takagi water heater is a warning sign for error code 991. 

According to the manuals of all the models of this water heater brand, the error code is common for these models and the fixing procedure is also similar. So, I am providing a common troubleshooting process for this code that will help no matter which model of Takagi water heater you use. Those models include, 

  • Takagi H series
  • Takagi tankless CT-199
  • 140 Indoor and Outdoor water heater series
  • Takagi Series 110
  • 910/910 ASME
  • Takagi CX3 Series
  • Takagi tankless 540P (Indoor and Outdoor)
  • Takagi HX3 series

Possible Reasons & Solutions For Error Code 101 in Takagi Tankless Water Heater? [Quick Overview!]

Before getting into the long and detailed troubleshooting, let me give you a quick overview of the possible reasons for their solutions. 

Incorrect gas type used or pressure out of rangeCheck installation altitude using GPS or a smartphone. Consult a technician for reinstalling within permissible altitude.
Airflow blockages in intake/exhaust pipesInspect and clear debris from intake/exhaust pipes. Clean the exhaust pipe if corrosion is present.
Insufficient space between intake and exhaustMeasure and compare distances as per guidelines. Adjust installation or reposition terminals if needed.
Installation site at an altitude higher than recommendedThe presence of grease and dirt on burner or fan motor
Incorrect altitude DIP switch settingsRefer to the manufacturer’s guidelines for DIP switch adjustments based on altitude. Ensure correct configuration for installation site altitude.
The presence of grease and dirt on the burner or fan motorTurn off and cool down the water heater before inspection. Clean components if advised in the manual. Professional cleaning is recommended for sensitive components.

In the next segment, we will discuss the reasons and solutions in detail.

Takagi Tankless Water Heater Error Code 101 [Detailed Troubleshooting]

As you already know from the previous segment this error code is a warning sign for code 991 which is a sign of imperfect combustion. To get rid of this code, you have to follow the troubleshooting process given below. 

Step 1: Check The Gas Type

Takagi manufacturers suggest using specific types of gas in the water heater. The gas types are usually natural gas or propane. Whatever gas is recommended for your water heater model should be written on the rating plate. 

So, make sure to only use the gas type specified on the rating plate of the water heater. You have to also ensure that any gas regulators in use are functioning correctly and maintaining gas pressures within the specified range. 

Using gas with pressures higher than recommended could lead to serious accidents, so always exercise caution. Here is the recommended gas type and pressure chart for most models. 

Gas TypeMinimum gas pressureMaximum gas pressure 
Natural Gas4.0″ W.C. (1.00 kPa)10.5″ W.C. (2.61 kPa)
Propane8.0″ W.C. (1.99 kPa)14.0″ W.C. (3.48 kPa)

Step 2: Check For Blockage In The Intake Or Exhaust Air

Check the intake air inlet and exhaust air outlet one by one and take the steps mentioned below. 

Carefully examine this area for any potential blockages. Look for the following.

  • Debris: Check for leaves, dust, insects, or other particles that might have accumulated and obstructed the airflow.
  • Obstructions: Look for objects, like boxes, tools, or anything that shouldn’t be there.
  • Damage: Ensure that the intake components are not damaged or dented, as this can also impede airflow.
  • Corrosion: Check for signs of rust or corrosion on the exhaust components, as this can affect the airflow.

After that, If you find any blockages in the inlet or exhaust pipe, gently remove them to ensure proper airflow. Use a soft brush or vacuum cleaner to clear away loose debris, being careful not to damage any equipment.

If there is corrosion in the exhaust pipe, you have to clean it properly with a corrosion cleaner.

Step 3: Ensure Enough Distance Between Terminals

If your water heater uses a direct-vent system, see if there is a good amount of space between the air intake and exhaust terminals.

Here’s the process you need to follow to ensure this. 

  1. First, find the intake and exhaust terminals on your water heater.
  2. Using a measuring tape or ruler, determine the distance between the intake and exhaust terminals. 
  3. Consult the water heater’s user manual or any manufacturer’s guidelines that came with the unit. If you don’t have the user manual, no worries. Here’s a guideline for enough space for Takagi tankless water heater vent pipes. 
  • Ensure that exhaust terminations have a minimum clearance of 1 foot (305 mm) from any obstructions.
  • Maintain a distance of at least 1 foot (305 mm) between each intake terminal when there are multiple terminals.
  • For multiple exhaust terminals, keep a minimum space of 1 foot (305 mm) between each of them.
  • Unless local building codes specify otherwise, the exhaust termination should be positioned horizontally at a distance of at least 2 feet (610 mm) from any wall or surface.

The following picture might help you with a clear understanding.

intake and exhaust terminal of takagi tankless water heater
  1. Compare the actual distance between the intake and exhaust terminals with the minimum requirement specified in the guidelines. If the measured distance meets or exceeds the recommended distance, you’re in good shape, and there’s sufficient space between the two terminals. 

If you find that the distance between the intake and exhaust terminals is less than what is recommended, you need to take corrective action. This involves adjusting the installation or repositioning the terminals to achieve the required separation. If you’re not sure about how to adjust the installation, it’s advisable to consult a professional technician.

Step 4: Check The Altitude 

The altitude of the installation site can impact the efficiency of certain types of water heaters, especially gas or propane heaters. At higher elevations, there is less oxygen in the air, which can affect combustion.

To check the altitude or elevation, you need to know how high above sea level the installation site is. Some GPS devices or smartphones with GPS capabilities can provide elevation data for your specific location.

The highest certified or permitted installation altitude for Takagi tankless water heaters is 10,100 feet (3,078 meters) for indoor models and 6,000 feet (1,829 meters) for outdoor models.

If your heater is installed at a higher altitude than this, you must consult a technician and reinstall the heater within the permissible altitude. 

Step 5: Check The DIP Switches Adjustments

Once you are ensured that the heater is installed within the right altitude range, it is time to check if the altitude DIP switches on the heater are correctly configured to correspond to the elevation. 

Here’s a guideline for the DIP switch adjustment for different altitudes. 

For indoor Models

takagi tankless water heater indoor models DIP switch adjustment

For outdoor models

takagi tankless water heater outdoor models DIP switch adjustment

Based on the altitude of your installation site and the guidance from the manufacturer’s manual, adjust the altitude DIP switches to the appropriate settings.

Step 6: Inspect The Burner And The Fan Motor

Inspect the burner and the fan motor of the heater for the presence of grease and/or dirt, especially if the water heater is located in an area where contamination is a concern.

Ensure that the water heater is turned off and completely cooled down before you begin any inspection to prevent any accidents or burns. 

Carefully inspect the burner area for the presence of grease and dirt. Look for any accumulation or build-up on the burner itself. Grease and dirt can accumulate over time and may impact the efficiency of combustion. Similarly, inspect the fan motor for any signs of grease or dirt.

If you find grease and dirt on the burner or fan motor, it’s advisable to clean these components. However, these are very sensitive components of the water heater. So, according to the Takagi Manuals, it is advisable to have them cleaned only by professionals or call the Takagi Technical Service Department. They also advise having these components checked for dirt and grease at least once a year. 

By completing all these troubleshooting steps, you should be able to get rid of the error code 101 in your Takagi tankless water heater. 


What is the error code 991 on a Takagi tankless water heater?

Error code 991 on a Takagi tankless water heater generally indicates an issue with the combustion. To resolve this, you have to make sure the inlet and exhaust pipes are blockage-free and the heater is installed in the proper space. 

What is error 391 on the Takagi water heater?

The error code 391 on a Takagi water heater indicates an “Air-fuel Ratio Rod failure in the heater. Examine the wiring and electrical connections related to the rods and make sure that there are no loose or damaged wires that could be affecting the sensor’s operation.

What is the Takagi tankless water heater error code 711?

Error code 711 on a Takagi tankless water heater indicates a “Gas Solenoid Valve Drive Circuit Failure. Inspect the wiring and connections related to the gas solenoid valve and its control circuit. Ensure that all connections are secure and that there are no loose or damaged wires.

What is code 61 on the Takagi tankless water heater?

Code 61 on a Takagi tankless water heater indicates a “Fan Motor Fault”. Look for any loose or damaged wires that connect to the fan motor and fix them. Inspect the fan motor for dust buildup. If there’s a lot of dust, clean it off.


Here are all the solutions for the Takagi tankless water heater error code 101 issue. I hope the troubleshooting guideline was easy to understand and by using this, you could solve your error code problem. 

If you are confused about the process, don’t hesitate to consult a professional technician. And last but not least, always maintain safety precautions while working on the heater.

That’s all. Have a great day. 

If you are further interested in repairing heaters on your own, read our article on Takagi tankless water heater leaking.

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