Thermostat calls for heat but boiler does not fire

Safety: This involves mains wiring. Isolate power at the fused spur and verify dead before opening the boiler or receiver.

Diagnosis:

• Confirm on the thermostat display that it is actually calling for heat (heating icon or flame symbol).
• At the receiver, observe whether the heating LED or relay indicator lights when heat is requested.
• With power off, check continuity of the switched live wire from the receiver output to the boiler's control input terminal.
• Verify that the boiler is configured to accept external control from a room thermostat and that any internal link has been removed or fitted as required by the Glow‑worm wiring diagram.

Remedy:

• Repair or replace any damaged wiring between receiver and boiler.
• If the receiver relay does not operate despite a valid RF signal, replace the Glow‑worm RF receiver.
• After repair, test by commanding heat from the thermostat and confirming boiler ignition.