Goodman Gas Furnace: GMP
Re: Multiple Attempts to Fire
The gas furnace burners ignite and shut-off several times before eventually burning normally.
Qty |
Possible Causes: |
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Low Flame Signal |
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Pressure Switch Fault |
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Bad Control Board |
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Thermostat Issue |
CHECKOUT:
1. Check Diagnostic Indication
- If it is possible, try to catch the burners cycling & check the diagnostic indication on the control board.
- Furnace Cycling Off and No Diagnostic = "W" Dropping Out, Low Flame Signal or Bad Control Board
- Place a jumper between "R" and "W" and re-check.
- Furnace Runs Normally = Thermostat Issue
- Furnace Still Cycles & No Fault Indication = Low Flame Signal or Bad Control Board → Step 3. Check Flame Sensor
2. Check Pressure Switch
- Monitor for 24VAC across the two "Yellow" wires attached to the pressure switch.
- 24VAC Present = Switch "Open"
- No 24VAC = Switch "Closed"
- Check the rated pressure of the switch.
- Place a pressure gauge in-line with the pressure switch hose.
- Monitor the pressure as the furnace operates.
- Pressure at or near the rating and the switch opens = Restricted Vent or Inducer
- Pressure well above the rating and the switch opens = Bad Pressure Switch
3. Check Flame Sensor
- On the multi-meter:
- Switch the test leads to "COM" and "mA".
- Set the meter on DC 200ù.
- Disconnect the wire from the flame sensor.
- Place one meter lead on the flame sensor terminal and the other on the flame sensor wire.
- 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) but Shuts Off = Bad Control Board
- MOVE SENSOR LEADS BACK TO "COM" and "V" BEFORE PROCEEDING!