Ruud
Control / Thermostat Runaway
Boiler runs continuously and overshoots the 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 relay on control board, miswired thermostat, shorted thermostat cable, failed temperature sensor
How to Fix / Troubleshooting
Safety first: Turn off power if the boiler will not shut down normally.
- Check thermostat operation: Turn the thermostat down below room temperature. If the boiler continues to run, remove the thermostat from its base. If the boiler still runs, the issue is in the boiler or wiring.
- Inspect thermostat wiring: Look for shorts between thermostat wires at the boiler terminals.
- Test sensors: Verify supply and room/outdoor sensors are reading correctly. Replace if faulty.
- Control board replacement: A stuck relay on the Ruud control board may require board replacement by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Main Control Board (Relay Section)
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