Sime
Uncontrolled Heating / Valve Stuck Open
Boiler heats radiators 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 motorised valve, Faulty room thermostat contacts, Incorrect wiring causing permanent call for heat, PCB relay stuck closed
How to Fix / Troubleshooting
Safety first: Radiators may become very hot; take care with children and vulnerable persons.
- Check programmer and thermostat: Ensure heating is set to off and thermostat is turned down. If radiators still heat, external controls may be bypassed.
- Feel motorised valve (if fitted): On systems with external valves, check if the valve is stuck in the open position. Sometimes moving the manual lever can temporarily close it.
- Engineer diagnosis: The engineer should test the room thermostat, wiring, motorised valves, and boiler PCB relay. Replace any component that is stuck or miswired.
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Repair Difficulty
Medium
3/5
Required Part
Motorised Zone Valve
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