Thermostat displays E05 and the boiler does not respond to heat demands.

Safety first: Isolate mains power to the boiler and receiver at the fused spur. The receiver usually contains live 230 V components.

Steps to check:

• 1. Verify wiring: Remove the receiver cover and compare wiring to the Baxi installation manual. Ensure COM and NO (or appropriate terminals) are correctly wired to the boiler’s room thermostat or control terminals.
• 2. Listen for relay click: With power restored and the front cover on, raise the set temperature. You should hear a distinct click from the receiver relay. No click may indicate a failed relay or control circuit.
• 3. Test switched output: If competent with electrics, measure voltage across the boiler control terminals when the thermostat calls for heat. If the relay does not close, the receiver is faulty.
• 4. Check for signs of overheating: With power off, inspect the receiver PCB for burn marks around the relay or terminals, which indicate contact failure.

When to call a professional: Relay replacement on the PCB is not typically user-serviceable. Replace the complete Baxi receiver module or have a heating engineer do so.