York furnace 1 red flash: Flame sensed with the gas valve off
One red flash means flame is being detected while the gas valve is off. Either gas is burning when it should not be, or the sensing circuit is reporting a flame that is not there.
Applies to: York, Luxaire and Coleman gas furnaces using the UTEC integrated furnace control boards documented in technical service letter ST-045-09. This code is stored in the error code array.
What it means
The control watches the flame sensor continuously, and detecting flame with the gas valve commanded off produces this code. It is treated seriously because one of the two possible causes is a gas valve that is not closing fully, meaning gas entering the combustion chamber outside a controlled cycle. The other is electrical: a short in the flame sensing circuit produces a signal the control cannot distinguish from a real flame. Since it cannot tell them apart, it assumes the dangerous one. York marks this code as stored in the error array, so it can be recovered from the history even after the furnace appears to recover.
Most common causes
- A gas valve leaking through or not closing fully.
- A slow-closing gas valve, where flame lingers after shutdown.
- A short to ground in the flame sensor wiring or at the sensor.
- A chafed or damaged sensor wire touching the cabinet.
- A failed control board misreading the flame signal.
- Residual flame on a burner after the main flame is cut.
How to diagnose it
- Confirm the colour is red. Amber patterns on these boards indicate normal heating states.
- Do not open the burner compartment while the furnace is powered.
- Note any smell of gas and act on it immediately rather than continuing.
- Have the stored fault history replayed, since this code is retained and its position in the sequence is informative.
How to fix it
- If you smell gas: leave the building, operate no electrical switches, and call your gas utility's emergency line or the fire service from outside.
- With no gas smell, switch the furnace off at its service switch and leave it off until a licensed technician has seen it.
- This is entirely technician work, involving the gas valve and the flame-sensing circuit.
- Do not reset repeatedly. If the valve is passing gas, each cycle is another opportunity for it to accumulate.
Notes
The wiring-short version is far more common than a leaking gas valve, and a technician usually finds it quickly. That does not make it safe to assume — the control cannot distinguish them and neither can anyone without test equipment at the valve.
Related
- 10 red flashes — Gas valve energised with no call for heat
- 8 red flashes — Lockout on recycles, flame dropouts