John Wood electronic gas water heater displays E010 and shuts down; no hot water

Safety: Turn off power before testing electrical components.

• 1. Locate the thermistor: On most John Wood electronic models, the temperature sensor is inserted into a well on the side of the tank and connected to the control by two wires.
• 2. Inspect wiring: Check the sensor wires for cuts, abrasions, or melted insulation. Repair or replace damaged wiring.
• 3. Test resistance: Disconnect the sensor from the control and measure resistance with a multimeter. Compare to the temperature/resistance chart in the service manual. A reading of 0 ohms (short) or infinite (open) indicates a bad sensor.
• 4. Clean connectors: If resistance is correct, clean the sensor and board connectors with electrical contact cleaner and reconnect firmly.
• 5. Replace sensor: If the sensor is out of spec, install a new John Wood thermistor rated for your model. Clear the code by power cycling and verify normal operation.