The short answer
A York furnace code is the light blinking in the little window on the lower door, and the number of red flashes names the safety check that shut your heat off. In Northern Virginia homes, three come up most: 3 red flashes (the pressure switch never closed, usually a blocked vent, a backed up drain or a tired inducer), 7 red flashes (no flame after three tries, usually the flame sensor, the igniter or the gas) and 4 red flashes (it overheated, usually a clogged filter). Change the filter, check the vent and drain, power cycle once, and call if the same count comes back.
How to read the light
Most York gas furnaces have a single status light on the control board, and you read it through the window in the blower door. Leave the door on: taking it off opens a safety switch and cuts the power.
A slow green flash means it has power and nothing is calling. A slow amber flash means the thermostat is calling for heat and everything is normal. Red flashes are faults. Each flash is about a third of a second on and a third off, then a pause, then the count repeats. Count it twice before you look it up.
The board also keeps its last five faults, and a tech plays them back with the LAST ERROR button, handy when the furnace is running fine by the time we arrive.
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York furnace flash codes
From York’s TM8E and TMLE installation manual; the single-stage TM9E prints the same chart.
Swipe to see all columns →
Swipe to see all columns →
| Light | What it means |
|---|---|
| Slow green flash | Normal: powered, no call for heat |
| Slow amber flash | Normal: the thermostat is calling and it’s heating |
| 1 red | Flame sensed with no call for heat. Shut off the gas |
| 2 red | Pressure switch closed when it should be open |
| 3 red | Pressure switch open when it should be closed: inducer, vent, hose or switch |
| 4 red | Main limit opened: the furnace overheated, filter first |
| 5 red | Rollout switch opened; it resets by hand, and it needs a tech |
| 6 red | Pressure switch opened four times in one call; locks out for an hour |
| 7 red | No flame after three tries; locks out for an hour |
| 8 red | Flame lost five times in one call; locks out for an hour |
| 9 red | Power polarity, ground or transformer wires reversed |
| 10 red | Gas valve powered with no call for heat. Shut off the gas |
| 11 red | Main limit open more than five minutes, usually the blower motor or wheel |
| 4 amber | The thermostat is calling for cooling without calling for the fan |
| Steady on, any color | The control board failed |
The four you’re most likely to see
3 red flashes: it hums but never lights
What you notice: The inducer fan near the top runs, but the burners never light.
What causes it: Before the gas opens, the inducer pulls air through the vent and a pressure switch closes to prove the path is clear. Three flashes means the switch stayed open. York’s own list: a failing inducer, a blocked vent pipe, a broken or disconnected hose on the switch, loose wires or the switch itself. On a high-efficiency York with white PVC pipes, a backed up condensate drain does the same thing.
What you can do: Clear snow, leaves or a nest from the PVC pipes where they leave the house, look for standing water in the drain hose and trap, then power cycle once.
When to call us: If it comes back, or the inducer sounds rough. The York pressure switch guide goes through every cause in order.
7 red flashes: three tries, then it quits for an hour
What you notice: You hear the inducer and the igniter, but no flame, or a flame that won’t hold. After three tries the furnace goes quiet for an hour.
What causes it: York lists the gas valve switch left off, low or no gas pressure, a dirty or failed flame sensor, a cracked hot surface igniter, a bad gas valve, loose wires or a burner problem.
What you can do: Make sure the gas handle on the pipe beside the furnace runs in line with the pipe, then power cycle once.
When to call us: If it locks out again. The York flame sensor guide covers the most common cause.
8 red flashes: it lights, then drops out
What you notice: The burners light, run a few seconds and go out, over and over, and the house never warms up.
What causes it: The flame was lost five times in one call for heat. York points at low gas pressure, a dirty or failing flame sensor, or the gas valve. The sensor is the usual one.
What you can do: Power cycle once to clear the one-hour lockout.
When to call us: If it’s back to 8 flashes by evening: the sensor needs cleaning or replacing.
4 red flashes: it overheated
What you notice: The burners shut off and the blower keeps running, often blowing cool air.
What causes it: The main limit switch opened because the furnace got too hot. York lists a dirty filter first, then ductwork that’s too small, the wrong blower speed, the wrong firing rate, loose wiring or a failing blower motor.
What you can do: Change the filter and open every supply vent and return.
When to call us: If it trips again with a fresh filter. 11 red flashes is the same switch staying open longer than five minutes, which York ties to a failed blower motor or blower wheel. Our York blower motor guide covers that part.
Codes that mean stop
1 red flash (flame with no call for heat) and 10 red flashes (gas valve powered with no call for heat) both mean gas may be flowing when it shouldn’t. Turn the furnace off at its switch and close the gas valve by turning the handle across the pipe. If you smell gas, don’t touch any switches: leave the house and call your gas company from outside. If the CO alarm is sounding, get everyone out and read what to do when the CO alarm goes off.
5 red flashes is the rollout switch beside the burners: flame came out of the burner box. It resets by hand, but don’t reset it yourself. Something pushed the flame out, and York’s list includes the combustion air, the inducer and a failed heat exchanger.
Two-stage and modulating York furnaces
The two-stage, variable speed TM9V reads most counts the same way. These are the ones that differ or are added, from its installation manual:
Swipe to see all columns →
Swipe to see all columns →
| Light | What it means on a TM9V |
|---|---|
| Continuous amber | Flame signal under 1.5 microamps: clean the flame sensor, check the gas flow |
| 5 red | Limit circuit open more than 15 minutes, usually a hand reset rollout switch |
| 11 red | Limit open 5 to 15 minutes, usually the blower motor or wheel |
| 12 red | Model ID plug loose or missing |
| 13 red | High fire pressure switch open: usually a partly blocked vent or a loose wire |
The modulating YP9C also uses amber flashes as warnings while it keeps heating: 4 amber means it turned itself down for an airflow restriction like a dirty filter or closed registers, 5 amber means it turned down for a blocked vent or air pipe or a clogged condensate drain, and a rapid amber flash means the flame sensor reads low (YP9C manual).
How to reset a York furnace
Set the thermostat to off. Turn off the breaker or the switch for the equipment, wait about five minutes, turn it back on and set the thermostat back. Do it once. That clears the one-hour lockouts (6, 7 and 8 red). If the same count comes back, the reset already told you what it can: a part is failing. A steady light that returns after a power cycle means a new control board, since York says the board isn’t field repairable.
Coleman and Luxaire, and who makes York now
York, Coleman and Luxaire furnaces have long come out of the same company: a 2001 safety recall covered furnaces sold under all three names. Bosch has run the home heating and cooling business behind York since July 31, 2025 (Bosch announcement), using the York name under a long-term license from Johnson Controls. Bosch lists Coleman and Luxaire as its regional brands. If your furnace says Coleman or Luxaire, the label and the chart inside the door are still the ones to trust.
More furnace codes and symptoms
Other brands: Carrier, Goodman and American Standard furnace codes, or every brand in our error codes and warning lights guide. By symptom: a furnace blinking light, a furnace that won’t turn on, a clogged or frozen drain. Our York repair page has what usually breaks on a York and what we charge to fix it.
Book a York repair
Call (703) 997-9757 or book online. A diagnostic visit is $99, and the tech reads the code, finds the part that set it and gives you the price before any work starts. We answer day or night. Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. If someone already quoted you a new system, our free second opinion looks at it first. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
What does 3 red flashes mean on a York furnace?
The pressure switch didn’t close when the inducer started, so the furnace won’t light. The usual causes are a blocked vent pipe, a backed up condensate drain on a high-efficiency model, a cracked hose on the switch or a failing inducer.
What does 7 red flashes mean on a York furnace?
It tried to light three times and never proved a flame, so it locked out for an hour. Make sure the gas is on, power cycle once, and call if it happens again. The flame sensor, the igniter and the gas valve are the usual causes.
How do I reset my York furnace?
Set the thermostat to off, turn off the furnace switch or breaker for about five minutes, then turn it back on. Do it once. If the code comes back, a part is failing and another reset won’t fix it.
What does a slow green or slow amber light mean on a York furnace?
Both are normal. Slow green means it has power and is idle. Slow amber means the thermostat is calling for heat and the furnace is running normally.
Who makes York furnaces now?
Bosch bought the home heating and cooling business from Johnson Controls in 2025 and uses the York name under a long-term license. Bosch lists Coleman and Luxaire as its regional brands.
