Thermostat shows F.05 and heating cannot be enabled

Safety: The receiver/backplate is usually mains powered. Isolate power at the fused spur and verify dead before removing covers.

Steps:

• Identify whether your Glow‑worm smart thermostat uses an RF receiver (with a relay) or an eBus digital interface. The receiver is typically near the boiler.
• With power off, remove the receiver cover and visually inspect the PCB for burn marks around the relay or output terminals.
• Check that the load connected to the receiver (boiler switched live or zone valve) is within the rated current of the relay. Overloading can weld contacts.
• Restore power and, using the thermostat, command heating ON and OFF while listening for a click from the relay. No click or continuous click may indicate a stuck or failed relay.

Remedy:

• If the relay is stuck or the PCB is heat‑damaged, replace the complete Glow‑worm RF receiver or interface unit; the relay is not normally serviced separately.
• Ensure the connected boiler or valve wiring is correct and that no short circuits exist on the switched live output.
• After replacement, re‑pair the thermostat with the new receiver and test operation.
• If you are not confident working with mains wiring, use a qualified heating engineer or electrician.