John Wood Tankless Error Codes: Troubleshooting Tips

John Wood tankless water heaterJohn Wood tankless

Explore our comprehensive guide on troubleshooting John Wood tankless water heater error codes.

In this article, we explore the world of error codes, equipping you with the knowledge to effectively troubleshoot and resolve issues with your tankless water heater. By decoding these error codes, you will gain valuable insights into diagnosing problems and taking appropriate actions for optimal performance.

Specifically, we'll focus on error codes that commonly appear on high-efficient water heaters from the 240, 340, and 540 series.

Let's dive in and empower you to tackle any problems that may arise.

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Temperature controllerTemperature controller

John Wood tankless water heaters feature an advanced computer board with a self-diagnostic system, enabling you or a technician to easily identify internal unit issues. This convenient tool streamlines troubleshooting processes.

When a temperature remote controller is installed on a John Wood tankless water heater and there is an issue with water heating, it serves as a diagnostic tool by displaying a three-digit error code. This code provides valuable information for troubleshooting and identifying the specific problem affecting the unit's performance.

If a remote control is not present, you can rely on the green LED on the computer board of a water heater to indicate any issues. The LED will emit a series of one to six signals, effectively signaling the presence of a problem and providing a basic form of error indication.

John Wood tankless error codes explained

Assuming the John Wood tankless water heater has been properly and professionally installed, we can now address troubleshooting other potential issues related to its operation.

Before diving into the troubleshooting process, let's familiarize ourselves with the list of error codes that may appear on the unit. By understanding these error codes, we can effectively diagnose and resolve any problems that may arise.

Here is the comprehensive list of error codes:

Error code 031 (green LED flashes only once) – This error code typically points to an incorrect DIP switch setting. It is important to ensure that the DIP switches are properly configured to match the specific requirements of your John Wood tankless water heater. By verifying and adjusting the DIP switch settings as needed, you can rectify this issue and restore optimal functionality to your unit.

Error code 101 (green LED flashes five times) – The code signifies a problem related to improper combustion or issues with the venting system. This could be due to blockages or damage in the venting system or an air intake terminal placed too close to the exhaust terminal. Additionally, the burner system might require cleaning due to the presence of dirt and grease, or the unit may have been exposed to contamination. To address this issue, it is recommended to inspect and clear any obstructions in the venting system, adjust the air intake terminal, clean the burner system, and ensure the unit is free from any contaminants.

Error code 111 (LED three times flashes) – This error code appears when the ignition fails. To resolve this issue, there are several steps you can take. First, ensure that the Hi-Limit switch is functioning correctly and that the wires are securely connected and undamaged. Next, clean the flame rod to remove any soot or deposits that may be affecting the ignition process. Additionally, inspect the computer board to ensure it is not damaged, and check the heat exchanger for any signs of leakage.

Error code 121 (LED flashes three times) – If you encounter error code 121 on your John Wood tankless water heater, indicated by three flashes of the LED, it signifies a flame loss. This error code can have similar underlying causes as error code 111. Ensure that the Hi-Limit switch is functioning properly and that the wires are securely connected and undamaged. Clean the flame rod to remove any soot or deposits that could be interfering with the flame. Additionally, inspect the computer board for any signs of damage and check the heat exchanger for possible leaks.

Error code 311 (LED flashes two times) – Begin by inspecting the outlet thermistor and heat exchanger thermistor for any signs of dirt, damage or malfunction. Ensure that the wire connections associated with these thermistors are secure and undamaged. By thoroughly examining these components, cleaning, and verifying the integrity of the wire connections, you can effectively troubleshoot and resolve the issue related to error code 311 on your tankless water heater.

Error code 321 (LED flashes two times) – Check the inlet thermistor. First, inspect the wires for any loose connections or breakage that could be impacting the system's operation. Additionally, examine the thermistor for any debris that may have accumulated, as this can interfere with its proper functioning.

Error code 331 (LED flashes two times) – Start by verifying the outlet thermistor's proper functioning. Thoroughly examine it for any indications of damage or malfunction. Furthermore, inspect the wires connected to the outlet thermistor for any signs of looseness, breakage, or poor connections. Finally, carefully check the thermistor for any debris that might impede its performance.

Error code 341 (LED flashes two times) – Exhaust thermistor failure.  Inspect the thermistor for any signs of damage or malfunction. Additionally, check for any loose connections or breakage in the wires associated with the outlet thermistor. Lastly, examine the thermistor for the presence of debris.

Error code 391 (LED flashes two times) - Failure of the Air-Fuel ratio rod (AFR). First, check for any loose or broken wire connections associated with the system. Ensure that all connections are secure and undamaged. Second, inspect the Air-Fuel ratio (AFR) rod for the presence of soot or other deposits that may hinder its proper operation.

Error code 441 (LED flashes two times) - Flow sensor failure. First, ensure that the flow sensor wires are correctly connected and free from any damage. Next, check for any loose connections or breakage in the wires associated with the flow sensor impeller and remove any debris that may be affecting its performance. Additionally, verify that the shutoff valves on the hot and cold water lines to the water heater are fully open. Lastly, inspect the filter for any blockages or debris that may be impeding water flow.

Error code 510 (LED flashes six times) - Gas solenoid valve malfunction. First, check the wires associated with the gas solenoid valve and the computer board for any signs of damage or loose connections. Additionally, inspect the computer board for burn marks, which may indicate a more severe issue.

Error code 551 (LED flashes six times) – The same problems as with the 510 error code.

Error code 611 (LED flashes four times) – Fan motor problem. Check the connections, wires, and computer board for damages and looseness. Inspect the fan motor for any dust buildup that may impede its performance, and ensure that there are no burn marks on the computer board. Additionally, check for any frozen or corroded connectors that may be affecting the fan motor's operation.

Error code 651 (LED flashes four times) – Faulty flow adjustment valve fault. Check for any connection issues or breakage in the wires associated with the valve. Additionally, examine the valve for a locked motor drive caused by scale buildup and inspect for any signs of water leakage.

Error code 661 (LED flashes four times) – This error code appears only on 540H models that have an issue with the bypass valve. Check the wire connections and ensure the unit is not affected by the limescale buildup.

Error code 701 (LED flashes one time) – Computer board error. Check the wire connections.

Error code 711 (LED flashes one time) – Gas solenoid valve circuit failure. See the error codes 111 and 121.

Error code 721 (LED flashes six times) – Due to the problem with the false flame detection, check if the combustion chamber is sealed and if the unit drains the condensate (only indoor models).

Error code 741 – The water heater doesn't respond when the remote is used. Verify the model compatibility of the remote controller, inspect and secure the connections between the water heater and remote controller, and ensure a consistent and adequate power supply to the unit.

Error code 751 – The same problem as for error code 741.

Error code 761 – Easy-Link system miscommunication between the water heaters.

Error code 941 (LED flashes five times) - Exhaust temperature is too high. The maximum temperature of the hot water should be 140 F.

Error code 991 (LED flashes five times) – Improper gas combustion. Check and fix the exhaust and vent system if there is a blockage and incorrect air supply. The water heater might not be getting fresh combustion air, especially if it is installed in the contaminated area or intake is too close to the exhaust. Check if the unit is set at the right altitude?

If your John Wood tankless water heater doesn't work or experience problems like; no ignition, flame failure, no hot water, water is not hot enough, temperature fluctuation, and overheating, use this guide to learn how to troubleshoot the tankless water heater.


Troubleshooting John Wood tankless water heater error codes can sometimes be done as a do-it-yourself (DIY) task, depending on the complexity of the issue. Many error codes can be resolved by following the provided troubleshooting steps, checking connections, cleaning components, and ensuring proper power supply.

However, in cases where the problem persists or requires technical expertise, it is recommended to seek assistance from professionals.

Ultimately, the decision to attempt DIY troubleshooting or seek professional help depends on your comfort level and the specific circumstances of the problem.

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My water heater does not ignite when water goes through the unit?

To troubleshoot a John Wood tankless water heater that fails to ignite, ensure the flow rate is above 0.5 GPM (1.9 L/min) and clean the filter on the cold water inlet to prevent restrictions. Check for reverse or cross connections in the water supply lines and ensure the power button is on for remote or temperature controllers. Additionally, verify that the inlet temperature is not too high, as it might prevent activation

Why my fan motor is still spinning after operation has stopped?

It is normal for the fan motor to continue spinning after the operation has stopped on a John Wood tankless water heater. This additional running time, which typically lasts between 15 to 70 seconds, serves two purposes. Firstly, it allows for a quick re-ignition if needed. Secondly, it helps purge any remaining exhaust gas from the flue, ensuring proper ventilation. Therefore, if you notice the fan motor running for a short period after the unit has stopped operating, there is no cause for concern as this behavior is part of the normal functioning of the water heater.

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