F.19
Glow-worm
No Heating Circuit Detected
Thermostat displays F.19 and cannot detect any heating circuit
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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.
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Possible Causes
Thermostat configured for wrong system type (e.g. underfloor only), Disconnected heating zone module, Faulty wiring between thermostat and wiring center, Failed internal output driver
How to Fix / Troubleshooting
Safety: Isolate mains power to the wiring center and boiler before inspecting wiring.
Steps:
- In the installer menu, verify that the system type matches your installation (e.g. S‑plan, Y‑plan, combi, system with cylinder).
- Check that at least one heating zone module or relay is connected and powered.
- Inspect the low‑voltage control wiring between thermostat, wiring center, and any Glow‑worm zone modules for continuity and correct terminations.
- Restore power and test a manual call for heat from the thermostat, observing whether any relays or valves operate.
Remedy:
- Correct configuration and wiring errors. If no heating circuit is detected despite correct wiring, replace the thermostat interface or main thermostat unit.
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Repair Difficulty
Hard
4/5
Required Part
Glow-worm thermostat interface / wiring center
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