Bosch Tankless Water Heater Codes [Full List + How To Fix]

Bosch tankless water heaters use error codes to indicate specific problems with the unit. Some common error codes for Bosch tankless water heaters include:

  • EA: Ignition failure 
  • EC: The flame has been extinguished during the unit’s operation.
  • A0: Faulty water temperature sensor
  • C2: Excessive flue blockage, etc. 

There are many different error codes that can be displayed on Bosch tankless water heaters. The specific codes and their meanings can vary depending on the model and age of the unit.

This guide on Bosch tankless water heater codes provides information on those error codes. These error codes are used by Bosch tankless water heaters to indicate specific problems or malfunctions within the unit. 

What Is A Bosch Tankless Water Heater Error Code?

A Bosch tankless water heater error code is a notification that something is not working properly with the unit. When an error code appears, it indicates that there is an issue that needs to be addressed. Each error code corresponds to a specific problem. The code is designed to help technicians quickly diagnose and fix the issue.

Error codes can appear on the control panel or digital display of the Bosch tankless water heater. The meaning of each code can be found in the owner’s manual. Also, here you’ll get a list of error codes with a quick solution. Just scroll down…

Overview Of Common Error Codes Of Bosch Tankless Water Heater

Error CodeDescriptionSolution
AOWater temperature sensor loose or damagedTighten sensor wire connections or replace the water temperature sensor
A1Air temperature inside the cabinet is too highCheck for flue leakages and call a professional if necessary
A2External water temperature sensor loose or faultyCheck and tighten sensor wire connections or replace the sensor
A3Flue gasses temperature sensor disconnected or damagedCheck and reconnect the sensor wire connections or replace the sensor
A4Air temperature sensor loose or defectiveCheck and tighten sensor wire connections or replace the sensor
A5Condensing unit flue sensor disconnected or defectiveCheck and reconnect the flue sensor wiring or replace the sensor
A6Inlet cold water temperature sensor disconnected or faultyCheck and tighten sensor wire connections or replace the inlet cold water temperature sensor
A7Heat exchanger hot water temperature sensor detached/faultyCheck and replace the sensor wiring or the sensor itself
A8Outlet hot water temperature sensor wire is loose or faultyCheck and tighten sensor wire connections or replace the sensor
ADFlue blockage detected during startupReset the water heater, check for air and exhaust restrictions, and ensure the flue length is within the specific
BBFan calibration triggered due to missed ignitionsAdjust gas inlet pressure or perform gas and air tuning
BCSuccessive fan calibration with similar learned valuesAdjust gas inlet pressure or perform gas and air tuning
C1 or C2Excessive blockage during startupCheck and clean air intake/exhaust pipes, reset the water heater
C3Flow sensor unable to detect water recirculationCheck the pump and its connection, replace the recirculation pump if necessary
C5Bypass water valve disconnected or defectiveCheck and tighten the wire connection or replace the bypass water valve
C7Fan wiring disconnected or faultyCheck and tighten fan wire connections or replace the fan
E0Internal issue with the control unitReset the water heater, and replace the control unit if necessary
E1Hot water temperature exceeds 194°FDisconnect power and gas, purge hydraulic circuit or adjust setpoint temperature
E9Broken thermal fuseReplace the thermal fuse
EAIgnition failure due to improper gas pressure or typeMeasure and adjust gas inlet pressure, ensure the correct gas type
ECFlame lost during operation due to improper gas pressureMeasure and adjust gas inlet pressure, perform gas and air tuning
bosch tankless water heater codes

Bosch Tankless Water Heater Codes [38 Error Codes Explained]

This Bosch tankless water heater error code guide covers the meaning, causes, and resetting of various error codes. It will cover a brief explanation of those error codes that can be encountered on Bosch tankless water heaters.

01. Error Code A0

Loose or damaged water temperature sensors trigger the error code “AO” on the controller display of a Bosch tankless water heater.

How To Fix:

To troubleshoot the error code “AO” on a Bosch tankless water heater, the first step is to check the sensor wire connections and tighten them if loose. To resolve the error code, hire a certified plumber or technician who specializes in Bosch tankless water heaters. They should replace the temperature sensor to prevent harm.

02. Error Code A1

If the air temperature rises above 158 °F, the appliance will automatically regulate its power output to prevent overheating. Additionally, the error code A1 will flash on the display to alert the user of the issue.

How To Fix:

If the Bosch Tankless Water Heater is displaying error code A1, the first step in troubleshooting is to ensure that the external air temperature is below 140 °F. 

Look for flue leaks within the water heater as well as in the concentric vent to determine whether the temperature is within the acceptable limit or not. If a leak is detected, it is highly recommended to seek the assistance of a professional to solve the issue. Flue leakages can be dangerous and require proper expertise to address.

03. Error Code A2

When the external water temperature sensor gets loose or is placed incorrectly, the Bosch tankless water heater will show fault number A2. Additionally, a faulty external water temperature or issues with the sensor itself can also trigger this error.

How To Fix:

If the exterior water temperature sensor’s wire connection is discovered to be loose, it should be examined and adjusted. If the wire connections are damaged, they should be replaced.

Additionally, the temperature sensor should be checked for proper installation. If tightening the wire connections or reinstalling the temperature sensor does not resolve the issue, the sensor should be replaced.

temperature sensor of bosch tankless water heater

Check if the recirculation settings are properly selected. You can select the correct recirculation settings through the following steps:

Step 1: On your Bosch tankless water heater, locate the control panel or display screen. Press the buttons labeled “+” or “-” to scroll through the options until you reach the recirculation program menu.

Step 2: Once you are in the recirculation program menu, you will see different options displayed on the screen. Use the buttons labeled “+” or “-” to navigate through the available options. The options include:

  • OF OFF: This option turns off the recirculation program.
  • Hr House Recirculation: This option enables the house recirculation mode.
  • It shows the available schedules: This option displays the available schedules for the recirculation program.
  • tI Tank Loading Internal NTC: This option enables tank loading using the water heater’s inlet water temperature sensor.
  • tE Tank Loading External NTC: This option enables tank loading using an external temperature sensor.
  • tA Tank Loading Aquastat: This option enables tank loading using an external aquastat.
  • Exit: This option allows you to exit the recirculation program menu.

Step 3: To select a desired mode, perform a long press on the button indicated as the selection button (usually labeled with a checkmark or an “OK” symbol). Hold the button until the desired mode is selected.

Step 4: If you wish to exit the recirculation program, press the buttons labeled “+” or “” to select the “E” or “Exit” option.

Step 5: Press the selection button (long press) to confirm and exit the recirculation menu.

Step 6: The recirculation program will be exited, and the water heater will return to its normal operation.

04. A3 Error Code 

The error code A3 on a Bosch tankless water heater is an indication that the flue gas temperature sensor is disconnected or damaged.

How To Fix:

The wire connections of the temperature sensor should be checked and reconnected tightly. If necessary, the sensor should be replaced, and the error code should be reset.

05. Error Code A4

The Bosch tankless water heater displays error code A4 when the air temperature sensor becomes loose or defective.

How To Fix:

To fix this issue, first check the wire connections of the sensor and tighten them. Change the sensor with a new one if the problem continues. 

06. Error Code A5

When the condensing unit flue sensor loses connection or develops a fault, diagnostic code A5 is shown on the controller.

How To Fix:

Check the wiring of the flue sensor and ensure it is secure. Once the sensor wiring is reconnected, ignite the water heater. Flue sensors should be changed if the problem continues.

07. Error Code A6

The inlet cold water temperature sensor is detached or broken if the tankless unit shows failure code A6 on the controller. 

How To Fix:

The solution to this issue is similar to the other error codes mentioned earlier, such as A4 and A5. Simply inspect the water temperature sensor’s cabling and fix any loose wire connections. Replace the input cold water temperature sensor if tightening the wire does not fix the problem.

08. Error Code A7

The diagnostic code A7 on the controller display of your tankless unit is also related to a sensor or wiring issue. This error code suggests a broken or malfunctioning heat exchanger hot water temperature sensor.

How To Fix:

To address this problem, it is necessary to perform a thorough examination of both the sensor and its wiring. It is best to replace or tightly reconnect any loose or broken wire. Similarly, if the sensor itself is found to be defective, it must be replaced with a new one to eliminate the error code.

09. Error Code A8

The controller display of the Bosch tankless water heater will show error number A8 once the output hot water temperature sensor wire becomes defective or becomes loose.

How To Fix:

One should inspect the sensor wiring to ensure it is not loose and, if required, tighten it. Additionally, if the sensor itself is faulty, it should be replaced to eliminate the error code.

10. Error Code A9

When you come across error code A9 on your Bosch tankless water heater, it means that the output power is lower than the required level for proper functioning. This issue can lead to inadequate heating of water or insufficient water flow.

How To Fix:

To troubleshoot error code A9 on your Bosch tankless water heater, follow these steps:

Step 1: Verify gas inlet pressure: Check the gas inlet pressure to ensure it meets the specified requirements. Follow the below steps to check gas inlet pressure- 

  • Shut off the gas supply: Use the shutoff valve provided by the installer. To turn off the gas supply specifically for the water heater.
  • Connect the manometer: Locate the gas inlet pressure test port. Loosen the screw inside the test port fitting without removing it. Connect the manometer tube to the test port.
  • Perform the static pressure test: Turn the gas supply back on and record the static gas pressure reading.
  • Perform the dynamic pressure test: Turn on the water heater. Access menu P1 Max. Power as described in the manual. Note that the appliance will run continuously at maximum power and allow maximum water flow.
  • Operate all other gas appliances (except the water heater) on the same gas piping system at maximum output.
  • Open all hot water taps to achieve a flow rate of at least 6 gallons per minute. If necessary, use one tub and two sinks to reach this flow rate. If the heater switches to P2 mode, open more hot water fixtures to maintain sufficient flow and keep the water heater in P1 mode.
  • Record the lowest operating gas pressure reading in a table.
  • Turn off the appliance, shut off the gas supply, and disconnect the manometer tube from the test point. Secure the test point. Tighten the screw inside the test point fitting to ensure it is secure.

Step 2: Inspect water temperature sensors and water flow sensor connections: Check the wire connections of the water temperature sensors and the water flow sensor. Ensure they are properly connected and secure. Loose or faulty connections can cause inaccurate readings and affect the performance of the water heater.

Step 3: Verify sensor specifications and replace it if necessary: Review the sensor specifications outlined in the product manual. If any of the sensors do not meet the specified requirements or if they are damaged, consider replacing them.

11. Error Code AD

The tankless unit shows error code AD when it detects a flue blockage during startup caused by insufficient combustion air.

How To Fix:

I advise holding down the power (on/off) button for three seconds to initially reset the water heater. This will initiate the startup sequence and clear the error code.

If restarting the water heater does not solve the problem, look for blockages in the air and exhaust openings. Additionally, ensure that the flue length is within the manufacturer’s specifications and that the air filter is clean and not blocked.

12. Error Code AA

If you receive error code AA on your Bosch tankless water heater, it indicates that the condensing unit’s flue gas temperature is above 392 °F (200 °C). The flue gas temperature at the exhaust sensor is also above 145 °F (63 °C). In response to this overheating condition, the appliance will regulate its power to prevent further damage or overheating.

How To Fix:

To troubleshoot the issue related to error code AA on your Bosch tankless water heater, you can perform the following steps:

i) Check the flue gas temperature sensor:

Inspect the flue gas temperature sensor for any signs of damage, disconnection, or malfunction. Ensure that it is properly connected and functioning correctly. If there are any issues, consider cleaning or replacing the sensor as per the manufacturer’s instructions.

ii) Check the water inlet temperature sensor:

Verify the condition of the water inlet temperature sensor. Ensure that it is securely connected and not damaged. Clean or replace the sensor if necessary.

iii) Descale the appliance:

Over time, mineral deposits can accumulate inside the water heater, affecting its performance. Follow the descaling procedure provided in the product manual to remove any scale buildup. Descaling helps maintain the efficiency of the water heater and can help resolve the overheating issue.

13. Error Code BB

The tankless unit displays the error code BB on the controller display due to missed ignitions, which trigger fan calibration. 

How To Fix:

Adjusting the gas inlet pressure or performing gas and air tuning will easily erase this error message. As previously stated, measure and adjust the gas input pressure according to the directions above mentioned in error code A9.

You have two choices for gas and air tuning: Automatic – UC Auto Adjust or Manual – MA Manual Adjust. The steps for carrying out an automated gas and air adjustment are listed below.

  1. You should choose the CA Combustion Settings menu and enter it in order to run the UC Auto Adjust. Then, select the UC menu through the Up or Down button, and then hit the OK icon to access this menu. Upon pressing the OK symbol, the automatic adjustment initiates immediately. 
  2. When the message “Open Taps” appears on the display, hot water faucets must be opened. 
  3. The unit will typically display this message five minutes after the automatic adjustment has started. 
  4. Wait for a green checkmark to be displayed, indicating that the automatic adjustment has been successfully completed. 
  5. Simply tap the back icon on the screen to leave the UC menu.

14. Error Code BC

Consecutive fan calibration using equivalent learning settings results in error code BC.

How To Fix:

To reset this diagnostic code, you can apply the same remedy mentioned for resetting the error code BB. In other words, you must change the intake gas pressure or execute gas and air adjustments to clear the error code BC.

15. Error Code C1 Or C2

Excessive blockage during startup will trigger the Bosch Tankless Water Heater to flash the error code C1 or C2. This occurrence is typically caused by insufficient combustion of air.

How To Fix:

Firstly, inspect the air intake and exhaust pipes and terminals for any restrictions that may cause excessive blockage during startup. If necessary, clean those piping to allow proper airflow for combustion.

Reset the water heater by simply holding down the on/off button for a period of three seconds after removing the obstruction from the exhaust tube. Check the air filter for any dirt or debris, and verify sure the flue length is within specifications.

By replacing the air filter if necessary and performing gas and air tuning, you can troubleshoot error codes C1 or C2 on your Bosch tankless water heater. 

  1. Check the air filter: Verify the condition of the air filter. If it is dirty or clogged, replace it with a new one. A blocked air filter can restrict airflow, leading to error codes C1 or C2.
  2. Perform gas and air tuning: It is recommended to perform gas and air tuning on the water heater. This involves adjusting the gas and air mixture to ensure optimal combustion. You can check the error code BB where I’ve explained how to perform air and gas tuning.

16. Error Code C3

The C3 error code will appear on your water heater’s display if the flow sensor is unable to detect water recirculation. Whenever the recirculation circuit is blocked, the pump or its connection malfunctions, or both, this problem occurs.

How To Fix:

First, check the pump and its connection. If the connection is loose, tighten it up. If needed, replace the recirculation pump. Additionally, verify the recirculation circuit for any blockages.

17. Error Code C5

If the diagnostic code C5 appears on the controller display, it means that there is a disconnected or defective bypass water valve. In simpler terms, the wire connection of that valve may have come loose or the valve itself may have gone bad.

How To Fix:

To resolve error code C5, start by examining the wire connection of the bypass water valve. Replace the wire entirely or tighten it up if the connection has become loose.

Replace the bypass water valve if the previous procedure does not resolve the problem. For the purpose of changing the bypass water valve, it is advised that you contact a trained expert. Following the replacement, do the following actions to calibrate the bypass water valve:

  1. To enter the AU technical settings menu, click the back symbol on the panel until you get the P4 Information screen.
  2. The AU technical parameters can be chosen by using the up or down button.
  3. Press the OK symbol to bring up the authentication menu, and enter the password (1886) to complete the authentication process.
  4. Before moving on to the following step, turn on a hot water faucet to confirm that water is flowing. In the PA menu, select the OK symbol and choose the MF main valve using the up or down button.
  5. Press the OK symbol to initiate the auto-calibration of the main valve. Please note that the water flow will shut off during the calibration process. Watch the display until the green check mark denoting a successful auto calibration for the main valve appears.
  6. Finally, touch the back symbol on the display to exit the AU technical settings menu and return to the main menu.

18. Error Code C7

The tankless unit displays fault code C7 if the fan wiring becomes disconnected or if there is an issue with the fan itself.

How To Fix:

Firstly, the wire connections of the fans need to be examined. If the wiring is loose, tighten it or replace it. If replacing the wiring doesn’t solve the issue, proceed to replace the faulty fan with a new one. It’s recommended to hire a professional to perform the replacement.

19. Error Code C8

If you receive error code C8 on your Bosch tankless water heater, it indicates that the main water valve is either disconnected or damaged.

How To Fix:

To troubleshoot the error code C8 on your Bosch tankless water heater, follow these steps:

i) Check the wire connections of the main water valve: Ensure that the wire connections to the main water valve are secure and properly connected. Make sure there are no loose or damaged wires that could cause a disconnection.

If the problem persists:

i) Replace the main water valve: If the wire connections are intact and the issue persists, consider replacing the main water valve. Faulty valves can cause the error code C8.

ii) Check the wire connections: During the valve replacement, inspect the wire connections again to ensure they are properly installed and connected.

iii) Proceed with main water valve calibration: After replacing the valve, follow the calibration procedure specified in the product manual to ensure accurate operation.

20. Error Code C9

The tankless water heater displays error code C9 when there is a fault with the barometric pressure sensor.

How To Fix:

Holding down the on/off button for three seconds will reset the error. The electronic control unit (ECU) should be changed if the problem persists.

21. Bosch Tankless Water Heater Error Code CA

The error code CA is displayed when the water flow exceeds 9.2 gallons per minute (gpm).

How To Fix:

To address error code CA, which indicates water flow above 9.2gpm, follow these steps:

  1. Clear the hydraulic circuit of air by disconnecting the appliance and doing so.
  2. Activate a water flow restrictor.
  3. Verify that the water pressure is no more than 150 psi.

Note: The maximum water pressure for the tankless water heater is 150 PSI (10.3 bar), and the minimum recommended water pressure is 18 PSI (1.2 bar).

22. Error Code CE

Error code CE indicates that the appliance has detected excessive flue blockage during operation, which is caused by excessive pressure on the siphon. As a safety measure, the appliance shuts down.

How To Fix:

Pressing and holding the on/off button for three seconds will reset the error. If the issue continues, look for blockages in the terminals and exhaust pipes before resetting the error. Additionally, see whether the air filter needs to be cleaned or replaced if it is dirty or blocked.

First, verify that the flue length conforms with the requirements before correcting the problem. If the problem persists, perform the gas and air tuning procedure which is described in the earlier section.

23. Error Code CF

Error code CF indicates that during operation, the appliance has detected excessive flue blockage caused by insufficient combustion air. As a safety measure, the appliance shuts down.

How To Fix:

To solve the error code CF, you can simply follow the instructions given in error code “CE”.

24. Error Code E0

If there is an issue with the control unit, the display will show the fault code E0. It is clear from this that the control unit has an internal issue. 

How To Fix:

To resolve this issue, start by resetting the water heater. Resetting the device requires three seconds of holding down the on/off button. The control unit should be changed if the error message still appears after the tankless unit has been reset.

25. Error Code E1

The diagnostic code E1 will appear on the water heater if the hot water temperature exceeds 194 °F. Additionally, the burner will be automatically turned off by the water heater to prevent scalding. The water heater will be reactivated once the unit has cooled down.

How To Fix:

To resolve the error code E1 on your water heater, take the following steps:

  • First, disconnect the unit from both the electric power and gas supply. 
  • The hydraulic circuit should then be purged to remove air. 
  • Additionally, you can try reducing the setpoint temperature to minimize temperature instabilities.

26. Error Code E2

An Error Code E2 typically indicates an issue with the cold water temperature sensor in the water heater. When the error code E2 is displayed, it usually means that the incoming water temperature is below 36°F (2°C).

This could be caused by a problem with the cold water supply, such as the water being too cold or a blockage in the water line. Additionally, it could be due to a faulty cold water temperature sensor or a malfunctioning water valve.

How To Fix:

If you suspect a problem with the cold water temperature sensor, you can inspect the wiring and measure the resistance to determine if the sensor or the water valve is faulty. Here’s how you can proceed:

i) Locate the cold water temperature sensor:

Consult your Bosch manual or technical documentation to find the exact location of the cold water temperature sensor. It is usually located near the inlet where the cold water enters the appliance.

ii) Inspect the wiring:

Check the wiring connected to the cold water temperature sensor for any signs of damage, loose connections, or corrosion. Ensure that the wires are securely connected to the sensor and there are no visible issues.

iii) Measure the resistance:

With the power to the appliance turned off, use a multimeter set to the resistance (ohms) measurement mode. Disconnect the wires from the cold water temperature sensor and connect the multimeter leads to the sensor terminals.

Measure the resistance and compare it to the recommended range specified in your appliance’s manual. If the measured resistance is significantly different or falls outside the recommended range, it may indicate a faulty sensor that needs to be replaced.

iv) Protect the appliance from freezing:

If the incoming water temperature is below 36°F (2°C), it’s important to take steps to prevent freezing. Freezing water can damage the appliance and its components. You can consider insulating the water lines or providing a heat source in the vicinity of the appliance to prevent freezing.

Consult the appliance’s manual or contact the manufacturer for specific instructions on protecting your appliance from freezing.

27. Error Code E3

Error code E3 indicates that the appliance has detected flue gas temperatures above 167 °F (75 °C) or sustained temperatures above 145 °F (63 °C) for two minutes. As a safety measure, the appliance cuts off the burner to prevent overheating.

How To Fix:

To resolve error code E3, begin by descaling the appliance by following this link. After descaling, reset the error by pressing and holding the on/off button for three seconds.

Consult the Bosch tankless water heater manual to determine the sensor’s resistance if the issue continues. Replace the sensor if the resistance is not within the acceptable range.

28. Error Code E4

If the air temperature inside the cabinet of your Bosch tankless water heater exceeds 176 °F (80 °C) or remains above 158 °F (70 °C) for two minutes, an error code E4 will appear. Also, the appliance’s burner will automatically cut off to prevent overheating.

How To Fix:

To start troubleshooting the E4 error code, look inside the cabinet to see if there are any concentric vents or flue gas leaks. Holding down the on/off button for three seconds will reset the error if there is no leakage.

When the error still occurs, check the sensor resistance and replace it if it doesn’t meet the requirements.

29. Error Code E5

If the condensing unit flue gas temperature on your Bosch tankless water heater exceeds 428 °F (220 °C) or remains above 392 °F (200 °C) for 2 minutes, the appliance’s burner will automatically cut off to prevent overheating.

How To Fix:

To address the issue with your Bosch tankless water heater, follow these steps:

  1. Perform a descaling procedure. Descaling helps remove mineral deposits and scale buildup, which can affect the performance of the water heater.
  2. Press and hold the on/off button for 3 seconds to reset the error code. This may clear any temporary issues or glitches.
  3. If the problem persists after descaling and resetting the error then check the sensor resistance (refer to the manual to find the sensor resistance specification). Measure the resistance of the sensor using an appropriate device. If the sensor’s resistance is not within the specified range, it may indicate a faulty sensor. In that case, replace the sensor.

30. Error Code E7

If you encounter error code E7 on your Bosch tankless water heater, it indicates an internal error with the electronic control unit.

How To Fix:

To troubleshoot the error code E7 on your Bosch tankless water heater, follow these steps:

  1. Reset the error. After resetting the error, observe the water heater’s operation to see if the E7 error code reappears. If the error code does not appear again and the unit functions normally, the issue may have been resolved. However, if the error code persists, continue to the next step.
  2. If the error code continues to appear after resetting, it is likely that there is a more serious issue with the electronic control unit. In this case, it is recommended to replace the electronic control unit.

31. Error Code E8

The error code “E8” indicates an error during the ionization test and an internal error in the electronic control unit. 

How To Fix:

Given that error code E8 specifically indicates an internal error in the electronic control unit, it is likely that replacing the unit will be necessary.

32. Error Code E9

The main reason behind the error code E9 on the controller display is a broken thermal fuse.

How To Fix:

The thermal fuse needs to be changed. It is best to get advice from a specialist if you are unsure of how to proceed.

33. Error Code EA

The error code EA indicates an ignition failure, which occurs due to improper inlet gas pressure. It should be noted that supplying the unit with the wrong gas type can also lead to ignition problems in your water heater.

How To Fix:

Follow the steps outlined at the beginning of this guide, gauge the gas inlet pressure, and adjust it accordingly. Then, verify that the water heater is being fed with the correct gas type – natural gas if it requires gas, or LP gas if not. Perform gas and air tuning as well.

34. Error Code EC

The error code EC indicates that the flame has been lost during operation. This problem can occur due to incorrect gas inlet pressure. In addition, wrong gas and air adjustments can also cause the water heater to display this error message on the controller.

How To Fix:

To resolve the error code EC, first connect a manometer and measure the gas inlet pressure to verify if it’s within the specifications. If not, it’s better to call a professional to adjust the gas inlet pressure. Next, perform gas and air tuning to eliminate the error code EC.

35. Error Code EF

The error code EF indicates that the wrong gas (LP instead of NG) is connected to the current appliance configuration.

How To Fix:

Inspect the type of gas to solve this error code. You can check it very easily by following our Bosch maintenance guide for tankless heaters which is linked above in the Error Code E3 section.

36. Error Code F2, F3, F7, F8 & F9

Bosch Tankless Water Heater throws Error Code F2, F3, F7, & F8 due to an internal error in the electronic control unit. 

How To Fix:

To resolve these error codes (F2, F3, F7, & F8), first reset the error by pressing and holding the on/off button for 3 seconds. If the error persists, check if the appliance’s configuration is correct by following the manual for Bosch tankless water heater. Next, you have to make an automatic combustion adjustment.

The electronic control unit must be replaced if the error code still appears on the display.  

37. Error Code F9

If you receive error code F9 on your Bosch tankless water heater, it indicates an internal fault with the gas valve driver. 

gas valve of bosch tankless water heater

How To Fix:

To troubleshoot the F9 error code on your Bosch tankless water heater, follow these steps:

Step 1: Inspect the wiring connections to the gas valve and ensure they are securely connected. Look for any loose or damaged wires and make sure they are properly connected. If you find any loose connections, tighten them appropriately.

Step 2: After checking the wire connections, test the system to see if the F9 error code persists. Turn on the water heater and monitor its operation. If the error code reappears, proceed to the next step.

Step 3: If the F9 error code continues to appear after checking the connections, it is likely that there is a problem with either the wire connections or the electronic control unit.

In this case, it is recommended to replace the wire connections and/or the electronic control unit. Contact Bosch customer support to obtain the appropriate replacement parts and seek assistance with the replacement process.

38. Error Code FA

The error code FA denotes the presence of a gas leak in the gas path, more specifically in the gas valve or gas manifold shut-off valves.

How To Fix:

Gas valve and/or gas manifold replacement is necessary. After replacing the gas valve and/or gas manifold, perform gas and air tuning as mentioned in an earlier section.

Bosch Tankless Water Heater Other Problems That Can Pop Up On Display

i) Thermal System Error

The display shows the solar thermal system symbol, but there is no solar thermal system present. The appliance’s minimum output power is higher than the power demand, which is the reason for this issue.

How To Fix:

To resolve the issue of power demand being lower than the minimum output power of the appliance, the hot water flow needs to be increased or the setpoint temperature needs to be adjusted to a higher value.

ii) Low Water Flow And Temperature

The appliance displays the symbols for low water flow and low temperature. This issue is occurring because the power demand is lower than the minimum output power of the appliance.

How To Fix:

To fix the problem of the appliance’s power demand being lower than the minimum output power, you should increase the hot water flow or adjust the setpoint temperature to a higher value.

iii) The Display Is Showing “–”

The display and the electronic control unit are not communicating with each other.

How To Fix:

You can try resetting the appliance by unplugging it for at least 10 seconds and then plugging it back in. The display, wire connections, and/or electronic control unit might need to be replaced if the issue continues.

iv) The Appliance Is Producing High-Pitched Noise Or Whistling Sound.

Either an excess of gas or a lack of air is indicated by the combustion flame.

How To Fix:

Inspect the gas type by following the below steps:

  • Simultaneously press and hold buttons +, , or p for 3 seconds. The display will show P4 for information. 
  • Use the buttons +, , or p to navigate and select P7 for Gas Type.
  • Press the button P to enter. 
  • Select the appropriate gas type according to the table mentioned below by using buttons + or
Gas TypeDisplay
Natural GasNA
Liquid PropaneLP
  • Press the button P for 3 seconds to confirm the gas type selection. The selected gas type will blink to indicate that it has been confirmed.

Check the gas inlet pressure as outlined in the previous section “Error Code A9”. If it keeps happening, perform gas and air tuning.

v) Making Low-Pitch Noise

The appliance is producing a low-pitch noise accompanied by vibration, commonly referred to as “rumbling.” This is because the combustion flame indicates either an excess of air or a lack of gas.

How To Fix:

By following the instructions in the previous section, you can determine if the gas type is correct. Also, if the issue persists, perform gas and air tuning. Additionally, check the gas inlet pressure as instructed in the previous section.

Precautions While Dealing With Bosch Error Codes

Precautions to be taken while dealing with Bosch error codes are:

Step 1: If you are unsure or uncomfortable with the troubleshooting procedures, seek the assistance of a qualified professional to avoid further complications.

Step 2: To reset the error, make sure all water taps are fully open with no restrictions. Then close all the taps and wait a few seconds before reopening them. This should reset the error.

Step 3: To reset the error, close and open all hot water faucets up to three times per hour. It’s crucial to remember that you shouldn’t perform this process more than three times an hour. During this process, the appliance will check for blockages and perform automatic air tuning, which may take up to three minutes.

Step 4: The display will show information about the problem and whether the appliance is locked for safety reasons. After resolving the issue, the error may need to be reset by pressing and holding the power button for three seconds. The appliance can be restarted using either the controls inside the appliance or the remote control.

Resetting A Bosch Tankless Water Heater After Troubleshooting

Resetting the water heater is a simple remedy for erasing an error code. To reset a Bosch tankless water heater, you need to press the red buttons located on the thermal cutouts of the heating elements. If you require additional assistance with resetting your Bosch tankless water heater, we have a comprehensive guide which is linked here & provides step-by-step instructions.

FAQs:

Can I fix an error code on my Bosch tankless water heater myself?

It’s not advisable to fix Bosch tankless water heater error codes by yourself unless you’re experienced with water heaters and repair procedures. It’s best to call a professional technician to diagnose and fix the problem.

How often do Bosch tankless water heaters experience error codes?

Depending on the unit’s age and maintenance history, Bosch tankless water heater error codes can appear more or less frequently. Error code occurrence is more likely to be decreased with routine maintenance and cleaning.

How often should I service the water valve on my Bosch tankless water heater?

It is recommended to service the water valve every 2-3 years. Regular servicing helps prevent problems caused by sediment or debris accumulation, ensuring smooth operation and optimal performance.

When should I have my Bosch tankless water heater’s gas and tuning serviced?

Gas and tuning adjustments for a Bosch tankless water heater should be performed during the initial installation and periodically thereafter. It is generally recommended to have a professional technician perform these adjustments every 1-2 years to ensure optimal performance.

Wrapping Up

When it comes to maintaining the optimal performance of your Bosch tankless water heater, understanding its error codes is crucial. With a whopping 38 different error codes, it’s understandable if you feel a bit overwhelmed when trying to diagnose and resolve any issues that arise. 

Following our Bosch tankless water heater error codes guide will ensure that you will be able to solve all the error codes that your water heater can show. As there are no error codes that pop up when your water heater doesn’t get hot enough. So you can have a look at our comprehensive guide on why Bosch tankless water heater not hot enough to solve the issue.

Also, you can check out our solution guide on Bosch tankless water heater pilot light issues in case you face any pilot light problems with your water heater.

Good Luck!

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