Gosund
Stuck Relay or Incorrect Differential
Thermostat shows correct mode but HVAC equipment runs continuously and does not shut off at setpoint
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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 closed heat or cool relay on thermostat, Differential set too wide, Short between R and W/Y in wiring, Furnace control board fault
How to Fix / Troubleshooting
Danger: Turn off power to the HVAC system immediately if equipment will not shut off.
- Step 1 – Observe thermostat output:
- Check if the thermostat still indicates a call for heat/cool when the setpoint is reached.
- Step 2 – Adjust differential:
- In settings, reduce the temperature differential to a normal value (e.g., 0.5–1.0°C).
- Step 3 – Inspect wiring:
- Look for shorts between R and W/Y at the thermostat and furnace board.
- Step 4 – Test without thermostat:
- Disconnect W/Y at the thermostat; if equipment continues to run, the issue is in the furnace/air handler.
- If it stops, the thermostat relay may be stuck.
- Step 5 – Replace thermostat if relay is stuck:
- Replace the thermostat if its internal relay remains closed even when no call is indicated.
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Repair Difficulty
Hard
4/5
Required Part
Heat/Cool Output Relay on Main Control PCB
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