York TM9V080B12MP11 Error Code 1 Red Flash: Flame Sensed Without Call for Heat
What Does Code 1 Red Flash Mean?
This code is set when the flame sensor detects a flame while the thermostat is not calling for heat and the gas valve is supposed to be fully closed. On this York two-stage furnace the board treats that as a safety event: it energizes both the inducer motor and the supply-air blower to purge the heat exchanger and cabinet of combustion products rather than leaving unexpected flame unattended.
The cause the manual points to is a gas valve that is leaking or slow to close. Valve seats and the solenoid seal can wear over many cycles, letting a small amount of gas pass after the valve is commanded shut; that gas can reach a still-hot ignitor or burner surface and light. Because this two-stage model uses a staged gas valve, a seat that no longer seals fully on shutdown is exactly the kind of fault that produces flame with no active call.
This is the mirror image of the 10 Red Flashes code, which reports the gas valve being electrically energized without a call for heat; here the valve is not commanded on, yet flame is still present, which points at gas leaking through the valve rather than at a wiring fault energizing it.
What You'll Notice
- Burner flame or heat is present when the thermostat is off or satisfied.
- The blower and inducer run unexpectedly, even though no heat was requested.
- The furnace seems unable to fully shut down between cycles.
- A faint gas odor may be noticeable near the furnace in some cases.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Leaking or slow-closing gas valve | Most common | ✗ Call a pro → |
How This Is Diagnosed
This is a gas-side fault and is diagnosed by a technician. They confirm the board is genuinely reading flame with no heat call (rather than a shorted flame-sensor wire falsely reporting flame), then focus on the gas valve: checking whether it leaks by or closes slowly on shutdown, and inspecting the valve and its seats. Because the safe repair is replacement of a leaking gas valve, and diagnosing a gas leak is not homeowner work, the inspection stops at identifying the source rather than adjusting the valve.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The furnace shows flame or heat when the thermostat is not calling for it — treat this as urgent.
- You smell gas near the furnace at any time: leave the home first and call your gas company, then arrange service.
- The blower and inducer keep running with no heat demand and the code stays present.
Frequently Asked Questions
Is a 1 red flash code dangerous?
It should be treated as a safety concern because it points to gas reaching the burners when the valve should be closed. Shut the furnace off at the breaker and have a technician inspect the gas valve promptly.
Why did my furnace's blower turn on by itself with this code?
The control board intentionally runs the blower and inducer as a safety measure to clear the heat exchanger and cabinet when it detects flame without a call for heat.
Can I fix a leaking gas valve myself?
No. Gas valve inspection and replacement are not homeowner tasks. This repair must be done by a qualified HVAC technician.
✓ Verified against manufacturer service manual — March 2026