Thermostat shows F.10 and backlight flickers or unit reboots randomly

Safety: This fault may involve mains voltage. Isolate power at the fused spur and verify dead before removing any covers. If you are not trained, do not work on mains wiring.

Diagnosis:

• Check the installation manual to confirm whether your Glow‑worm thermostat is battery powered, 24 V, or 230 V powered.
• At the backplate or receiver, verify that the correct supply voltage is present using a multimeter and that it is connected to the correct terminals.
• Look for signs of overheating or discoloration on the thermostat backplate or receiver PCB.
• If the thermostat is battery powered, replace batteries and ensure the contacts are clean and not corroded.

Remedy:

• Correct any mis‑wiring immediately. Never connect 230 V to low‑voltage eBus or sensor terminals.
• If the thermostat still shows F.10 after wiring is corrected and power is stable, the internal power supply circuit is likely damaged; replace the thermostat head or receiver.
• If a separate 24 V transformer or wiring center supplies the thermostat, test and replace that transformer if its output is unstable.