Ruud
Thermostat or Low-Voltage Control Circuit Failure
Thermostat calls for heat but furnace does nothing, LED on board is on solid, no inducer or blower.
Advertisements
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.
Advertisements
Possible Causes
Broken thermostat wire between furnace and thermostat, Faulty thermostat, Loose R or W connection at control board, Blown low-voltage fuse
How to Fix / Troubleshooting
Safety: Turn off power before touching thermostat wiring at the furnace.
Steps to check:
- Verify thermostat settings: Ensure the thermostat is set to HEAT and the setpoint is above room temperature. Replace batteries if applicable.
- Check low-voltage fuse: Inspect and replace the 3–5A fuse on the control board if blown.
- Test furnace response: With power off, remove the thermostat wires from R and W at the furnace. Restore power and temporarily jumper R to W at the board. If the furnace starts, the thermostat or thermostat cable is likely faulty.
- Inspect wiring: Look for staples driven through the thermostat cable or visible damage along its path.
Advertisements
Repair Difficulty
Medium
3/5
Advertisements