F.18
Glow-worm
Safety Lockout from Boiler Fault
Thermostat shows F.18 and heating demand is locked out
Advertisements
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Advertisements
Possible Causes
Boiler reporting persistent lockout via eBus, Incorrect boiler fault mapping in thermostat, Communication glitch causing stale fault status, Boiler PCB fault
How to Fix / Troubleshooting
Safety: Boiler faults can involve gas and combustion. Do not remove the boiler combustion cover. Isolate power before accessing any terminals.
Steps:
- Check the boiler’s own display for an error code. Refer to the Glow‑worm boiler manual to identify and address the boiler fault first.
- Once the boiler fault is cleared and the boiler is reset, check whether F.18 clears automatically on the thermostat.
- Power‑cycle both the boiler and thermostat to clear any stale fault flags on the eBus.
Remedy:
- If the boiler operates normally but the thermostat still shows F.18, there may be a communication or mapping issue. Update thermostat firmware if available.
- If the problem persists, a Glow‑worm engineer should check both the boiler PCB and thermostat interface module.
Advertisements
Repair Difficulty
Hard
4/5
Required Part
Glow-worm boiler PCB / eBus communication
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements