HeatingCodes

York TM9V furnace flash codes

By Jason Dearmin · Last reviewed November 14, 2026

This York furnace has a single diagnostic LED on the control board that flashes red, green or amber. The color and the number of flashes tell you what the control found.

What this table coversFlash codes from the York TM9V*C (two-stage, variable-speed, 96% AFUE) installation manual. Other York and Coleman furnaces use different controls and different code lists, so check your model number first.

How to read the display

A slow flash lasts 2 seconds on and 2 seconds off. A numbered code flashes the LED on for one-third of a second and off for one-third of a second, the number of times in the code, then pauses for 2 seconds and repeats for as long as the fault remains. Six red flashes means six quick red blinks, a pause, and again.

York says the control has a soft lockout that resets automatically after one hour, which protects an empty house from a short interruption such as a gas supply problem. A hard lockout does not restart on its own. It needs power to the control turned off and back on.

York code table

CodeMeaningWhat the document says
Slow green Normal operation, no thermostat call
Slow amber Normal operation with a call for heat
LED off No LED flash at all Check for power to the board and for a blown fuse on the board. If the board has power and the fuse is good, the board may need to be replaced.
Steady on (any color) Control failure Turn power to the furnace off and back on. If the code returns, the control board must be replaced.
Continuous amber Flame sense current is below 1.5 microamps Clean the flame sensor and check gas flow (technician work).
1 red Flame sensed when there was no call for heat The control turns on the inducer and blower. Check for a leaking or slow-closing gas valve.
2 red Pressure switch is closed when it must be open Faulty pressure switch or miswiring.
3 red Pressure switch contacts are open when they must be closed Faulty inducer, blocked vent pipe, broken pressure switch hose, disconnected wires or a faulty switch. Full explanation
4 red Main limit switch has opened The blower and inducer run. Dirty filter, duct problems and blower problems are the listed causes. Full explanation
5 red Limit circuit open for more than 15 minutes (usually a rollout switch) Hard lockout. Power must be cycled to reset after the problem is corrected.
6 red Pressure switch opened four times during one call for heat Check for a faulty inducer, a blocked vent pipe or a faulty switch. Locks out for 1 hour.
7 red Flame could not be established in three trials for ignition Locks out for 1 hour, then restarts. Full explanation
8 red Flame lost five times during the heating cycle Check for low gas pressure, a dirty or faulty flame sensor or a faulty gas valve. Locks out for 1 hour.
9 red Reversed line voltage polarity, a grounding problem or reversed low-voltage transformer wires The furnace will not start the ignition sequence until this is corrected.
10 red Gas valve energized with no call for heat Blower and inducer run and no ignition sequence starts while this exists.
11 red Limit circuit open for more than 5 and less than 15 minutes Usually a failed blower motor or blower wheel. Hard lockout.
12 red Loose or missing model ID plug
13 red High-fire pressure switch open when it must be closed Check for a partially blocked vent pipe or loose or disconnected wire.
4 amber Y signal from the thermostat without a G signal A thermostat wiring problem. The furnace still heats and cools normally.

Source: York TM9V*C installation manual 5750149-UIM-I-0423, Furnace control diagnostics.

Detailed explanations

SafetyThese tables describe what the manufacturer documents say. Gas, combustion, refrigerant and line-voltage repairs are for licensed professionals. If you smell gas, leave the building and call your gas utility or 911. Safety disclaimer.

Sources