ACV
Heating Demand Stuck On
Boiler runs continuously and does not turn off when room is warm
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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 PCB, Faulty room thermostat stuck closed, Incorrect wiring (permanent call for heat), Faulty zone valve end switch
How to Fix / Troubleshooting
Safety first: You may need to turn off the boiler at the isolator to stop heating until repaired.
- Check thermostat: Turn the room thermostat down to minimum or to OFF. If the boiler continues to run, the fault is likely in wiring, zone valves, or PCB.
- Check programmer: Set the heating program to OFF. If the boiler still runs, note this for the technician.
- Zone valve test: Feel the heating zone valve(s). If one is stuck open and its end switch is calling for heat, it may need replacement.
- Professional repair: A technician should test the PCB relays, thermostat, and zone valves, and correct any wiring errors.
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Repair Difficulty
Medium
3/5
Required Part
Main Control PCB
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