Boiler runs continuously and does not turn off even when thermostat is satisfied or turned down.

Safety first: Immediately isolate mains power to the heating system at the consumer unit or fused spur.

• Check receiver output: With power off, disconnect the switched live from the Drayton receiver. Restore power and confirm that the boiler no longer runs continuously. If it stops, the fault is in the receiver or wiring.
• Inspect wiring: Verify that the permanent live and switched live are correctly wired at the receiver and wiring centre according to the Drayton wiring diagram.
• Test relay: Command heat on and off while measuring continuity across the receiver’s COM/NO terminals (with power isolated). If continuity remains when off, the relay is stuck.
• Replace receiver or valve: Replace the Drayton receiver if the relay is stuck. If the receiver output is correct, investigate and replace any zone valve with a stuck end-switch.