HeatingCodesYork TM9V furnace 3 red flashes: pressure switch contacts open
What 3 red flashes means
The York TM9V*C installation manual describes it this way: "3 red flashes: this indicates the pressure switch contacts are open when they must be closed." It then lists what to check: a faulty inducer, a blocked vent pipe, a broken pressure switch hose, disconnected pressure switch or inducer wires, or a faulty pressure switch.
How to count: the LED turns on for one-third of a second and off for one-third of a second, the number of times in the code. There is a 2-second pause between codes. For three red flashes you will see red, red, red, a pause, then the same again.
The pressure switch codes together
| LED | Meaning (per York) |
|---|---|
| 2 red | Pressure switch is closed when it must be open. The control checks at the start of each heat cycle and will not continue if it is closed. Check for a faulty switch or miswiring. |
| 3 red | Pressure switch contacts are open when they must be closed. Check the inducer, vent pipe, hose, wires and switch. |
| 6 red | The pressure switch opened four times during a call for heat while the unit was operating. Check for a faulty inducer, a blocked vent pipe or a faulty switch. The furnace locks out for 1 hour and then restarts. |
| 13 red | The high-fire pressure switch is open when it must be closed. Check for a partially blocked vent pipe, a loose or disconnected wire and vent pressure. |
York adds a warning in the same section: never adjust the pressure switch to allow furnace operation.
The winter angle
This is a 96% condensing furnace, so it vents through plastic pipe to the outdoors. A blocked vent or intake pipe keeps the pressure switch open. Heavy snow, ice buildup and bird nests are all possible. The manual lists "blocked vent pipe" as a cause. You can look at the termination from the ground.
Safe homeowner checks for York furnace 3 red flashes
- Turn the thermostat offStop the heat call so the furnace does not keep trying to start.
- Check outdoor vent and intakeFrom the ground, clear snow, ice or debris from the vent and combustion air terminations. Do not climb on a roof or remove the pipes.
- Restart onceSet the thermostat to heat. If the LED returns to 3 red flashes, stop.
- Call a technicianSwitch, hose, inducer and wiring checks should be done by a qualified technician.
Frequently asked questions
Where is the LED on a York TM9V furnace?
It is on the control board. York says it can flash red, green or amber. Look through the sight window in the blower door if your furnace has one, and do not remove panels unless you are qualified.
Is 3 red flashes the same as 2 red flashes?
No. Two red flashes means the pressure switch is closed when it should be open. Three red flashes means it is open when it should be closed.
Will the furnace restart on its own?
York says 6 red flashes causes a 1-hour lockout and then a restart. For 3 red flashes, the manual does not give a lockout time, but the furnace will not light until the switch closes.
Sources
- Installation Manual 5750149-UIM-I-0423: Two-Stage Variable Speed ECM Residential Gas Furnaces, TM9V*C series (96% AFUE), Furnace control diagnostics (Johnson Controls (York)) Covers: York TM9V*C two-stage variable-speed 96% furnaces. Other York and Coleman furnace series use different boards and flash codes; check the label on your furnace.
Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.