On the covered York TM9V two-stage variable-speed gas furnace, 3 red flashes means the pressure switch contacts are open when they should be closed. First, look outside for a blocked intake or exhaust pipe termination, such as snow, leaves or a nest.
Differential
Likely causes of “York TM9V two-stage variable-speed gas furnace showing 3 red flashes”, and how to tell them apart
- 1
A blocked intake or exhaust pipe
What separates it The inducer runs but the furnace will not fire
How to confirm Check outside for snow, leaves or a nest
- 2
A pressure switch that is open when it should be closed
What separates it Three red flashes at the start of a cycle
How to confirm Technician testing
- 3
A pressure transducer fault
What separates it The pressure reading is wrong
How to confirm Technician testing
- 4
Condensate backed up in the lines
What separates it Water in the switch tubing
How to confirm Technician draining and inspection
- 5
A weak inducer
What separates it The inducer sounds slow
How to confirm Technician testing
Before you touch a setting
Record this first — changing settings destroys the evidence
- That the LED shows three red flashes
- Whether the inducer runs
- Whether the termination outside is clear
- Whether the code appears at the start of the cycle
Try in this order
0 of 8 completedWhat to do first
ReversibleLook outside for a blocked intake or exhaust pipe termination, such as snow, leaves or a nest.
Correct only the documented fault domain
ReversibleYork's manual says to check for a faulty inducer, a blocked vent pipe, a broken pressure switch hose, disconnected pressure switch or inducer wires, or a faulty pressure switch. The outside vent check is the safe one, and the rest is technician work.
Turn the thermostat down
ReversibleThen up to call for heat.
Listen for the inducer
ReversibleIt should start first.
Look outside
ReversibleAt both pipe terminations.
Clear snow or leaves
ReversibleWithout touching the pipes' fittings.
Restart
ReversibleAnd watch one cycle.
Call a technician
ReversibleIf it returns.
Model-specific
What is true of this model and not of its siblings
- What the switch proves
- Before the burners light, the inducer draws air through the heat exchanger and out the vent. The pressure switch senses that and closes. If it stays open, the control will not light the gas, since it cannot prove the vent is clear.
- Intake and exhaust
- On a high efficiency furnace there are two pipes outside. Snow drifts, leaves, a nest or a frozen discharge can block either, and a quick look is safe from the ground.
- The transducer
- York mentions a pressure transducer, which reads the pressure rather than switching, so a technician tests both.
- The sound
- A healthy inducer comes on with a steady hum. A grinding sound or no sound at all points to the inducer.
- Why not bypass
- Jumping a pressure switch removes the check that the vent works, which can fill the house with exhaust gas.
- After a storm
- Check the terminations once the weather clears, since drifting is common.
- Two pipes, two jobs
- A condensing furnace such as a TM9V draws combustion air in through one pipe and sends exhaust out through another. The two terminations usually sit side by side on an outside wall or the roof. Check that they are clear of snow, leaves, a bird's nest and dryer lint, and that nothing has been stacked in front of them.
- Why the inducer matters
- The inducer is a small fan that starts the flow before the burners light. If it runs but the switch stays open, the pressure is not reaching the switch, because of a block, a split hose or a failing switch. If the inducer does not run at all, a different fault is at work, and you should tell the technician which you heard.
- Plan for winter
- Keep a small shovel by the door for the termination. After a snowfall, clear the openings and keep the drift from rebuilding. If the termination is on the roof, ask a professional rather than climbing up.
Stop boundary
When this stops being a self-service repair
- !Never bypass, jumper or tape over a safety switch
- !Stop for a carbon monoxide alarm, soot, scorch marks or flame outside the burner compartment
- !Call a qualified technician for anything behind the furnace's panels
- !If you smell gas, leave the building and call the gas utility from outside; do not use switches or phones inside
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does 3 red flashes mean on a York TM9V two-stage variable-speed gas furnace?+
The pressure switch contacts are open when they should be closed.
What is the common outside cause?+
A blocked vent or intake.
Who tests the switch?+
A technician.
Is it safe to run?+
Not with the code showing.