York Furnace Blower Won’t Shut Off — What’s Happening
A York furnace blower that won’t shut off is a symptom, not a specific fault code. When the blower runs continuously even when the thermostat is not calling for heat or cooling, the control circuit is being told to run the fan or the fan relay is being held closed. In practical terms, this usually means the thermostat is intentionally commanding fan operation, the 24 V control circuit is being falsely energized, or a relay or sequencer contact has welded shut.
If the blower continues after a heat call ends, some furnaces run the blower during a timed off-delay or during a limit or safety event. If it never stops, that points to a fault rather than a normal purge cycle. York’s own troubleshooting guide points to thermostat settings, airflow, power, and filter checks as the first steps for this condition.
Most Likely Causes
- Thermostat fan setting on ON instead of AUTO The thermostat fan switch is set to ON, which commands continuous blower operation regardless of heating or cooling calls.
- Faulty thermostat The thermostat continues to send a fan signal on the G wire even when set correctly to AUTO.
- Thermostat wiring short or miswire A short or miswire between R and G wires can keep the blower commanded on continuously.
- Stuck or welded relay contacts The fan relay contacts on the furnace control board have welded shut and cannot open to stop the blower.
- Tripped or failed safety or limit switch An overheating or safety-limit condition from restricted airflow keeps the blower energized as a protective measure.
- Restricted airflow or dirty filter A clogged filter or blocked return or supply registers contributes to overheating and abnormal safety or blower operation.
- Control board or sequencer issue A failing control board or sequencer holds the blower output on even when no call is present.
How to Diagnose and Fix
- Verify the thermostat fan setting is on AUTO, not ON, and confirm the mode and setpoint are correct.
- Disconnect the thermostat from its base and observe whether the blower stops running. If it stops, the thermostat or its wiring is the problem.
- Inspect the thermostat wiring for shorts, damage, or miswiring, and check for unwanted continuity between the R and G wires when the thermostat is disconnected.
- At the furnace control board, check the G, Y, and W terminals to see if any call signal is present. If no call exists but the blower output remains energized, the relay or control board is likely failing.
- Inspect all safety switches and limit switches for open or tripped conditions, and determine why they opened. Correct the underlying overheating or airflow issue before replacing any switch.
- Check airflow components including the filter, registers, return and supply blockages, blower wheel condition, and duct restrictions.
- If relay contacts are welded or the board output is stuck, replace the defective relay or control board rather than bypassing it.
- After repair, verify the blower responds correctly in AUTO, during heat and cooling calls, and confirm the furnace completes its normal fan off-delay cycle.
Parts You Might Need
| Part | Notes |
|---|---|
| Thermostat | Amazon | Replace if proven faulty during disconnect test or wiring inspection. |
| Furnace control board | Amazon | Replace if relay output is stuck on or board does not respond to thermostat signals. |
| Fan relay | Amazon | Replace if contacts are welded or stuck closed. |
| Air filter | Amazon | Replace if dirty or clogged to restore proper airflow and prevent overheating. |
Related Error Codes
If your appliance also shows a code on the display, these match this problem:
When to Call a Pro
Call a professional if you are not comfortable working with 24 V control wiring or 120 V blower circuits, or if the blower continues to run after you have verified thermostat settings and wiring. A technician can safely diagnose relay and control board faults, test safety and limit switches, and correct any underlying overheating or airflow issues. If the furnace has tripped a safety limit or if you suspect a gas burner or ignition problem contributing to overheating, have a qualified HVAC technician inspect and repair the system. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.