York Gas Furnace: TG9S/GY9S

Re: No Heat - Flashing Code 12

Code 12 = Igniter failure

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.
    • No Glow from Glow Plug + Code 12 → Step 2. Check Glow Plug
  • 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