Slant/Fin
Boiler Overfiring / Control Failure
Boiler room is unusually hot, boiler seems to run constantly
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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 gas valve, Shorted thermostat wiring, Failed aquastat contacts on Slant/Fin boiler, Zone valve stuck open
How to Fix / Troubleshooting
Safety: If the boiler will not shut off, turn off power and gas immediately.
Steps:
- 1. Check thermostat: Turn thermostat to lowest setting or OFF. If boiler continues to run, suspect control or wiring.
- 2. Inspect thermostat wiring: Look for shorts between thermostat wires at the boiler or along their run.
- 3. Aquastat: If the burner runs even when water temperature is above setpoint, the aquastat contacts may be welded closed and require replacement.
Professional service: A technician must test the gas valve and safety controls to ensure safe operation.
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Repair Difficulty
Professional Required
5/5
Required Part
Aquastat Control
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