On the covered York TM9V two-stage variable-speed gas furnace, 6 red flashes means while the unit was operating, the pressure switch opened four times during the call for heat. The furnace locks out for one hour and then restarts. First, look outside for a blocked intake or exhaust pipe termination.
Differential
Likely causes of “York TM9V two-stage variable-speed gas furnace showing 6 red flashes”, and how to tell them apart
- 1
A blocked vent pipe
What separates it The switch opens during the call for heat
How to confirm Check outside for a block
- 2
A faulty inducer
What separates it The inducer slows or stops
How to confirm Technician testing
- 3
A faulty pressure switch
What separates it The switch opens with a clear vent
How to confirm Technician replacement
- 4
Condensate or ice in the vent
What separates it The furnace trips in freezing weather
How to confirm Technician inspection
- 5
A loose tube to the switch
What separates it The reading drops
How to confirm Technician inspection
Before you touch a setting
Record this first — changing settings destroys the evidence
- That the LED shows six red flashes
- Whether the furnace ran before the code
- The weather
- Whether the inducer sounds normal
Try in this order
0 of 8 completedWhat to do first
ReversibleLook outside for a blocked intake or exhaust pipe termination.
Correct only the documented fault domain
ReversibleYork's manual says to check for a faulty inducer, a blocked vent pipe or a faulty pressure switch.
Look outside
ReversibleAt both terminations.
Clear snow or leaves
ReversibleFrom the openings.
Wait out the lockout
ReversibleYork says one hour.
Listen for the inducer
ReversibleAt the next start.
Note how long it ran
ReversibleBefore the code.
Call a technician
ReversibleIf it returns.
Model-specific
What is true of this model and not of its siblings
- While it is running
- This code is about the switch opening during operation. The furnace lit and then lost the proof of airflow, which suggests a vent or inducer that weakened as the furnace warmed up.
- York's list
- York says to check for a faulty inducer, a blocked vent pipe or a faulty pressure switch.
- The inducer
- A tired inducer motor can start well and slow as it warms. A technician checks its speed and its current.
- Winter
- Ice at the discharge can build gradually and raise the vent's resistance over several minutes, giving this exact pattern.
- Safe checks
- Look from the ground; do not climb for a roof termination.
- Do not bypass
- A pressure switch must never be jumpered.
- Counting what the control counted
- Six flashes mean the pressure switch opened four times during one heating call. After the fourth, the control locks out for an hour. The furnace starts normally and then loses the proof of airflow, which tells you the problem develops while it runs.
- What heat does to an inducer
- An inducer motor that is worn may run well when cold and slow down as it warms, dropping the pressure. A technician measures the pressure with a manometer while the furnace runs and compares it with York's figures.
- A vent that changes with the weather
- A termination that freezes over or fills with snow gradually can start a furnace and then block it. If the code appears only on the coldest days, say so. A technician may recommend raising the termination or adding a guard where the local code allows it.
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 6 red flashes mean on a York TM9V two-stage variable-speed gas furnace?+
While the unit was operating, the pressure switch opened four times during the call for heat. The furnace locks out for one hour and then restarts.
How is it different from three flashes?+
Three is an open switch at start; six is one that opens while running.
What is the lockout?+
One hour, then a restart.
What causes it?+
A faulty inducer, blocked vent or faulty switch.
Can a blocked condensate drain cause six red flashes?+
Yes. Anything that restricts the vent path or lets condensate back up can open the pressure switch: a blocked pipe termination, a clogged condensate trap or drain, or a vent pipe that has sagged and holds water. Check outside for snow, leaves or ice on the pipes, and if the cause is not obvious, leave it to a technician rather than bypass the switch.