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TG9S/GY9S - Flashing Code 12

Article ID: 693
Last updated: 19 Nov, 2021

York Gas Furnace: TG9S/GY9S

Re: No Heat - Flashing Code 12

Code 12 = Igniter failure

Qty Possible Causes:
1 Bad Glow Plug
Bad Control Board


CHECKOUT:

1. Check Ignition Sequence

  • If the furnace is running, turn the thermostat off and allow the furnace to cool and the blower to stop operating.
  • Initiate a call for heat from the thermostat and monitor the ignition sequence.
    • 1. The inducer motor should start with no difficulty.
    • 2. The pressure switch should close within a couple seconds of the inducer starting.
    • 3. The glow plug should energize within 30 seconds of the pressure switch closing.
    • 4. The gas valve should open within 20 seconds of the glow plug energizing.

2. Check Glow Plug

  • Look for any visual cracks.
  • Unplug the 2-wire connector to the glow plug.
  • Use a meter to test the resistance of the glow plug.
    • No Resistance = Bad Glow Plug
    • Resistance ⇒ Temporarily plug-in a new glow plug (make sure it isn't touching anything), reset the board, restart a heat cycle, and re-check for a Code 12.
      • New Glow Plug Energizes = Bad Glow Plug
      • Still a Code 12 = Bad Control Board

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Article ID: 693
Last updated: 19 Nov, 2021
Revision: 3
Views: 95
Comments: 0