Takagi Error Codes

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Troubleshooting tankless water heaters and Takagi error codes. How to use diagnostic system to repair the faulty Takagi heater. Find the most frequent error codes and recommendations for the fix.


John Wood tankless water heaters are equipped with the advanced computer board and utilize the self-diagnostic system that allows you to check if the problem occurs inside the unit. It provides convenience and easy troubleshooting.

If the heater is equipped with the remote controller and something is wrong with the water heating, the three digit error code will appear. If there is no remote control the only thing what will indicate the problem will be a green LED on the computer board which will signal from one to six times.

How to use the Takagi error codes for troubleshooting

Assumption: the Takagi water heater was properly installed, per codes and manufacturer's recommendations. This includes electric, water and gas connections and vent flue installation.

Error code 031 (green LED flashes only once) – DIPswitch setting is incorrect.

Error code 101 (green LED flashes five times) – Problem with the improper combustion, venting system; it 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, grease or the unit might be in the contaminated area.

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 and make sure the computer board is not damaged and heat exchanger is not leaking.

121 (LED flashes three times) – Flame loss. The reason might be the same as for error code 111.

311 (LED flashes two times) – Depends on the model, check the outlet thermistor or heat exchanger thermistor and the wire connections.

321 (LED flashes two times) – Check the inlet thermistor.

331 (LED flashes two times) – Ensure proper work of the outlet thermistor.

341 (LED flashes two times) – Exhaust thermistor failure.

391 (LED flashes two times) - Failure of the Air-Fuel ration rod (AFR). Check the wire connection for looseness or breakage.

441 (LED flashes two times) -Ensure the flow sensor wires are properly connected and with no damage.

510 (LED flashes six times) – Gas solenoid valve malfunction. Check wires and computer board for damages.

551 (LED flashes six times) – The same as 510 error code.

611 (LED flashes four times) – Fan motor problem. Check the connections, wires and computer board for damages and looseness.

651 (LED flashes four times) – Faulty flow adjustment valve due to mineral buildup or wire damage.

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 build-up.

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

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

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

741 – Water heater doesn't respond when the remote is used.

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

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

941 (LED flashes five times) - Exhaust temperature is too high. Maximum temperature of hot water should be 140 F.

991 (LED flashes five times) – Improper gas combustion. Check and fix the exhaust and vent system if there is 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. Is the unit properly set for the right altitude?

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(Pictures courtesy of Takagi)

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