Glow-worm
Stuck Heating Relay / Bypassed Control
Boiler runs continuously even when thermostat is set low or off
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
Welded relay contacts in RF receiver, Permanent live linked directly to boiler call terminal, Zone valve microswitch stuck closed, Thermostat configured in monitoring‑only mode
How to Fix / Troubleshooting
Safety: Isolate mains power to the boiler and wiring center before working on wiring or receivers.
Steps:
- Turn the thermostat to OFF or set a very low setpoint and confirm that it is not calling for heat.
- At the receiver, check if the heating ON indicator remains lit even when there is no demand. If so, the relay may be stuck.
- With power off, disconnect the switched live from the receiver to the boiler. Restore power briefly: if the boiler now stops, the fault is in the receiver or wiring, not the boiler.
- Inspect any zone valves: a stuck microswitch can back‑feed a call for heat. Manually move the valve lever and listen for microswitch clicks.
Remedy:
- Replace a faulty RF receiver with welded relay contacts.
- Correct any incorrect permanent live links that bypass the thermostat.
- Replace any zone valve with a stuck microswitch.
Advertisements
Repair Difficulty
Hard
4/5
Required Part
Glow-worm RF receiver relay / heating zone valve
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements