Display shows E05 and heater will not start heating cycle

Safety first: Disconnect power to the heater before accessing the control compartment.

• Locate inlet sensor: Find the water inlet temperature sensor (NTC1) on the inlet pipe or heat exchanger manifold. It is typically a small probe with two wires.
• Inspect wiring: Follow the sensor cable to the control board. Look for cuts, abrasions, or rodent damage. Repair or replace damaged wiring.
• Clean connectors: Unplug the sensor connector at both ends (sensor and board) and inspect for corrosion or moisture. Dry and clean with electrical contact cleaner if needed, then reconnect firmly.
• Check sensor mounting: Ensure the sensor is fully inserted into its well or clamped tightly to the pipe for accurate readings.
• Reset power: Restore power and restart the heater to see if E05 clears.

If the error persists, the inlet NTC sensor is likely defective and should be replaced. If a new sensor does not resolve the issue, the main control board may be faulty and requires professional diagnosis.