Remeha
Uncontrolled heating / boiler firing without demand
Radiators get hot even when the room thermostat is turned down or off
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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
Stuck relay on main PCB, Faulty room thermostat, Shorted thermostat wiring, Diverter valve stuck in heating position (combi)
How to Fix / Troubleshooting
Safety first: Overheating can waste energy and damage components. Monitor system pressure and temperature.
- Check thermostat: Confirm that the room thermostat is actually turning off (display, click sound). Replace batteries if applicable.
- Isolate thermostat circuit: Turn off power and disconnect the thermostat wires at the furnace. Restore power; if the furnace still fires for heating, the fault is internal.
- Diverter valve check: On combi models, verify that the diverter valve is not stuck in the heating position. A technician may need to replace the valve motor or cartridge.
- PCB relay: If the heating relay on the PCB is stuck closed, the main control PCB must be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Main Control PCB
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