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TM9T Diagnostic Codes / Fault Codes

Article ID: 702
Last updated: 20 Apr, 2022

York Gas Furnaces: TM9T

Re: Diagnostic Codes / Fault Codes

These York gas furnaces have a control board inside the furnace blower compartment that will flash a diagnostic code that shows the operating status of the furnace.

Diagnostic Codes:
Slow Green Normal Operation - no call for heat
Slow Amber Normal Operation - with a call for HEATING
Rapid Amber Low flame signal
  • Flame signal below 1.5 microamps
  • Check flame sensor
  • Check gas pressure
4 Amber No Call for G.
  • Check low voltage wiring
Rapid Red Twinning error; incorrect phasing
  • Twinned furnaces must be on the same "phase" of power.  
  • Check voltage between the "Hot" legs of power of each furnace - should read 0 volts.
1 Red Flame present with gas off
  • Stuck gas valve
  • Shorted flame sensor 
  • Faulty control
2 Red Pressure switch stuck closed
  • Bad pressure switch
  • Inducer fan relay stuck on
3 Red Pressure switch stuck open
  • Bad pressure switch
  • Bad inducer fan
  • Bad inducer fan relay
  • Blocked or restricted vent
  • Condensate drainage issue
4 Red Limit switch open / open fuse
  • Bad limit
  • Low airflow
  • Over-Fired
5 Red Rollout switch open / open fuse
  • Bad switch
  • Cracked heat exchanger
  • Bad inducer motor
  • Over-Fired
6 Red

4 open pressure switch faults in one heating cycle

  • Bad pressure switch
  • Bad inducer fan
  • Bad inducer fan relay
  • Blocked or restricted vent
  • Condensate drainage issue
7 Red 3 failed ignition attempts
  • Bad igniter
  • Dirty flame sensor
  • No gas flow
8 Red Flame was established but later lost - 5 times in one heating cycle
  • Dirty flame sensor
  • Combustion air problem
9 Red Grounding or line polarity fault
  • Look for loose or missing Ground wire
  • Try reversing transformer power
10 Red Gas valve circuit shorted
  • Check gas valve wiring
11 Red Extended limit switch open
  • Bad limit
  • Blower failure
12 Red Igniter failure
  • Bad Igniter
  • Bad board

Fault Code Retrieval:  With no thermostat call push and release the LAST ERROR button.  The LED will flash up to 5 stored fault codes, beginning with the most recent.  If there are no codes in memory, the LED will flash two green flashes.

Clear the Fault Codes:  Push and hold the LAST ERROR button for at least five seconds.  The LED will flash three green flashes when the memory has been cleared.

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Article ID: 702
Last updated: 20 Apr, 2022
Revision: 3
Views: 18
Comments: 0