York 80% Gas Furnace: GY8S

Re: Won't Ignite

Failure to ignite should result in Flashing Code 7 = Lockout due to ignition retries. Caused by multiple failed ignition attempts.

► Code 7 is a Hard Lockout that disables heat operation and must be reset by cycling power to the furnace or by turning the thermostat off and back on.

CHECKOUT:

1. Check Ignition Sequence

• Reset the furnace, if necessary, by cycling power.
• 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 → Step 3. Check Glow Plug
  • 4. The gas valve should open within 20 seconds of the glow plug energizing.

2. Check Ignition

• Visually inspect the burners during ignition.
  • The burners should light smoothly with little or no delay from the glow plug to the flame sensor.
  • Make sure the flame sensor comes in good contact with the flame.
    • Burners Ignite Properly → Step 5.  Check Flame Sensor
    • Any Delay or Burners Not Igniting = Clogged Burners, Low Gas Pressure or Bad Gas Valve → Step 4.  Check Gas Pressure / Valve

3. Check Glow Plug

• Look for any visual cracks.
• Unplug the 2-wire connector to the glow plug.
• Use a meter to test resistance of the glow plug.
  • No Resistance = Bad Glow Plug
• Start an ignition sequence.
• Check for 120VAC power on the 2-wire plug feeding the glow plug during an ignition sequence.
  • No Power = Bad Ignition Control
  • Power Present but No Glow = Bad Glow Plug

4. Check Gas Pressure / Valve

• Inlet Gas Pressure
• Turn off power to the furnace and close the gas safety shut-off valve.
• Hook-up a gas pressure gauge to the inlet test port of the gas valve.
• Open the gas safety shut-off and check gas pressure.
  • Minimum Pressure = 5" w.c. for Nat. gas, and 11" w.c. for propane.
    • Low Pressure = Gas Supply Issue
• Re-apply power to the furnace and activate a call for heat.
• Make sure the inlet gas pressure stays above minimum when the gas valve energizes.
  • Pressure Drops Below Minimum = Gas Supply Issue
• Manifold Gas Pressure
• Turn off power to the furnace and close the gas safety shut-off.
• Move the gas pressure gauge to the manifold (leaving) test port on the gas valve.
  • CAUTION! Be sure to put the plug back in the inlet test port before proceeding!
• Open the gas safety shut-off valve and re-apply furnace power.
• Activate a call for heat and monitor the manifold gas pressure during an ignition attempt.
  • Normal Pressure = 3 - 3.5" w.c. for Nat. Gas, 9 - 11" w.c. for LP
    • No Gas Pressure = Bad Gas Valve
    • Low Gas Pressure ⇒ Increase Manifold Gas Pressure
    • Normal Gas Pressure + No or Delayed Ignition = Clogged Burners ⇒ Remove burners and clean spreaders