GMH95 / GCH9 - Flashing Code 1

​Goodman Gas Furnace: GMH95 / GCH9

Re: Flashing Code 1 / Won't Ignite

Code 1 = 3 Failed Ignition Attempts

► ** Be aware that the furnace Condensate Pressure Switch breaks power to the gas valve and will cause a Fault Code 1 (Does not cause a Code 3). **

CHECKOUT:

1. Check Ignition Sequence

• If necessary, reset the furnace lockout by cycling high voltage or low voltage power.
• Initiate a call for heat from the thermostat and monitor the ignition sequence.
  • The inducer motor should start with no difficulty.
  • The pressure switch should close within a couple seconds of the inducer starting.
  • The glow plug should energize within 30 seconds of the pressure switch closing.
    • No Glow from Glow Plug → Step 2. Check Glow Plug
    • Glow Plug Glows → Step 3. Check Ignition

2. Check Glow Plug

• Look for any visual cracks.
• 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 + No Glow = Bad Glow Plug

3. 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 Don't Ignite → Step 4. Check Control Board Output
    • Delayed Ignition or Some Burners Not Igniting → Step 5.  Check Gas Pressure/Valve
    • Burners Ignite Properly → Step 6.  Check Flame Sensor

4. Check Control Board Output

• Check Power from Control Board
• Re-start the furnace with a call for heat from the thermostat.
• At the point of ignition, check for 24VAC between Terminal 2 (Gray) and Terminal 9 (Brown) of the molex plug on the control board. 
  • No Power = Bad Control Board
  • Power Present ⇒ Continue
• Check Power at the Gas Valve
• Re-start the furnace with a call for heat from the thermostat.
• At the point of ignition, check for 24VAC between PM (Gray) and C (Brown) at the gas valve.
  • Power at the Gas Valve + No Ignition → Step 5. Check Gas Pressure/Valve
  • Power at the Board + No Power at the Gas Valve = Open Pressure Switch  (Clogged Drain) → Step 7. Check Furnace Drains

5. Check Gas Pressure / Valve

• Inlet Gas Pressure
• Turn off power to the furnace and check the inlet gas pressure.
  • Minimum Pressure = 5" w.c. for Nat. Gas, and 11" w.c. for Propane.
    • No or Low Pressure = Bad Meter or Regulator
    • Normal Pressure ⇒ Continue
• 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 = Bad Meter/Regulator or Restricted Gas Line
  • Normal Pressure ⇒ Check Manifold Gas Pressure
• Manifold Gas Pressure
• Activate a call for heat and monitor the manifold gas pressure during an ignition attempt.
  • Normal Pressure = 2.5 - 3.5" w.c. for Nat. Gas, 9 - 11" w.c. for LP
    • 24V on PM + 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

6. Check Flame Sensor

• DO NOT clean the flame sensor before testing!
• On the multi-meter:
  • Switch the test leads to "COM" and "mA".
  • Set the meter on DC 200ù.
  • Check the reading when the burners ignite.
    • Minimum acceptable reading = 1 MicroAmp
      • Low Reading ⇒ Clean Flame Sensor & Re-check
      • Normal Reading (2 to 6 mA) → Step 7. Check Furnace Drains
  • MOVE SENSOR LEADS BACK TO "COM" and "V" BEFORE PROCEEDING!

7. Check Furnace Drains

• Remove and check the drain hose from the collector box.
  • Water pours out = Clogged Drain Hose 
• Remove and check the drain hose from the exhaust elbow.
  • Water pours out = Clogged Drain Hose 
• Remove the Dip Tubes from the Furnace Drain Trap and make sure they are clear.

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