Controller shows E021 Coolant Heater Failure / Engine Heater Fault

Safety first: Isolate AC supply to the heater circuit before working on it. The heater operates on mains voltage.

• Check power supply: Verify the dedicated breaker or fuse for the engine heater is on and not tripped. Reset if necessary and monitor.
• Measure heater resistance: Disconnect the heater leads and measure resistance across the element. An open circuit indicates a failed heater that must be replaced.
• Inspect wiring and thermostat: Check for burnt connectors or damaged cables between the power source, thermostat, and heater.
• Confirm operation: After repair, energize the heater and verify current draw and a gradual rise in engine coolant temperature.

A non‑functional heater can cause hard starting and increased engine wear in cold climates; repair promptly.