Troubleshooting John Wood tankless water heaters. How to use a diagnostic system and fix the problems by using the error codes that appear on the remote controller/display.
The following error codes appear on water heaters from the 240, 340, and 540 series.
John Wood tankless water heaters are equipped with an advanced computer board and utilize the self-diagnostic system that allows you/technician to check if the problem occurs inside the unit. This is a convenient tool for simpler troubleshooting.
The three-digit error code appears if the heater is equipped with the remote controller and something is wrong with the water heating. If the remote control is not installed, the only thing that will indicate the problem will be a green LED on the computer board, which will signal from one to six times.
We will assume that the unit was properly/professionally installed (electric, water, gas connections, and per codes).
Error code 031 (green LED flashes only once) – DIP switch setting is incorrect.
Error code 101 (green LED flashes five times) – The problem is with the improper combustion, venting system which might be blocked or damaged, or the air intake terminal is too close to the exhaust terminal. The burner system might need some cleaning due to the presence of dirt and grease, or the unit might be exposed to contamination.
Error code 111 (LED three times flashes) – This error code appears when the ignition fails. Ensure the Hi-Limit switch runs properly and the wires are not loose or damaged. Clean the flame rod from soot and deposits, make sure the computer board is not damaged, and the heat exchanger is not leaking.
Error code 121 (LED flashes three times) – Flame loss. The reason might be the same as for error code 111.
Error code 311 (LED flashes two times) – It depends on the model but check the outlet thermistor, heat exchanger thermistor, and wire connections.
Error code 321 (LED flashes two times) – Check the inlet thermistor.
Error code 331 (LED flashes two times) – Ensure the proper work of the outlet thermistor.
Error code 341 (LED flashes two times) – Exhaust thermistor failure.
Error code 391 (LED flashes two times) - Failure of the Air-Fuel ratio rod (AFR). Check the wire connection for looseness or breakage.
Error code 441 (LED flashes two times) - Ensure the flow sensor wires are correctly connected and with no damage.
Error code 510 (LED flashes six times) - Gas solenoid valve malfunction. Check wires and computer board for damages.
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.
Error code 651 (LED flashes four times) – Faulty flow adjustment valve due to mineral buildup or wire damage.
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.
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 something 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.