Burnham
Boiler Fails to Shut Off on Temperature
Boiler runs continuously and overshoots thermostat setting, house becomes too 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 thermostat relay, Shorted thermostat wiring, Faulty aquastat or control, Zone valve end switch stuck closed
How to Fix / Troubleshooting
Safety first: Turn off power before working on controls or wiring.
- Check thermostat: Turn the thermostat down below room temperature or switch it to OFF. If the boiler continues to run, the issue is not the thermostat setting.
- Inspect thermostat wiring: At the boiler, remove one thermostat wire from the TT terminals. If the boiler stops, the thermostat or wiring is shorted.
- Check zone valves: A stuck end switch in a zone valve can hold the boiler on. Observe valve indicators and wiring; disconnect suspect end switch wires to test.
- Test aquastat/control: If the boiler continues to fire even with TT open, the internal control relay may be stuck and the control board or aquastat will need replacement.
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Repair Difficulty
Medium
3/5
Required Part
Aquastat Control
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