Goodman Gas Furnace: GMS8/GDS8/GHS8
Re: Short-Cycling / Won't Ignite - No Codes
The furnace starts an ignition sequence, then shuts-off and re-starts at the point of ignition.
Qty |
Possible Causes: |
2 |
Shorted Gas Valve |
|
Bad Ignition Control Board |
CHECKOUT:
1. Check Ignition Sequence
- 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.
- The gas valve should power within 20 seconds of the glow plug energizing and stay open for at least 5 seconds.
- Check for 24VAC across the two wires at the gas valve (while still connected).
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 Control Board Output
- Re-start the furnace with a call for heat from the thermostat.
- Ensure that the glow plug energizes.
- At the point of ignition, check for 24VAC between Terminal 9 (Blue) and Terminal 12 (Brown) of the molex plug on the control board.
- No Power = Bad Control Board or Shorted Gas Valve
- Power at Board + No Power at Gas Valve = Tripped Auxilairy Limit (Mounted in blower compartment) ⇒ Check limit and blower operation.
- No Power = Bad Control Board or Shorted Gas Valve → Step 4. Check Gas Valve
4. Check Gas Valve
- Remove the two wires from the gas valve.
- Re-start a call for heat and check for 24VAC power between the two removed wires.
- No Power at Controller + No Power at Gas Valve = Bad Ignition Control
- Power at Gas Valve ⇒ Temporarily plug the two wires into a new (uninstalled) gas valve and re-try an ignition sequence.
- Gas Valve Powers for at least 5 seconds = Shorted Gas Valve
- No Power to Gas Valve = Bad Ignition Control Board
Article ID: 623
Last updated: 14 Feb, 2020
Revision: 3
Equipment -> Gas Furnaces -> Goodman -> GMS8/GHS8/GDS8 -> GMS8/GHS8/GDS8 - Short-Cycling, Won't Light - No Codes
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