HVACopediaGoodman · Furnace troubleshooting
Delayed ignition - rough light-off
What is going on
Delayed ignition. Gas builds up in the chamber, lights late, thump. Gas work, licensed gas tech only. No bypassing safeties.
Likely causes
- Wrong gas pressure
- Burners not seated in their slots or not level
- Carry-over (lighter tube) blocked
- Burner orifice bent or out of line
Check in this order
- Qualified gas tech only. Never bypass or change safety controls.
- Check gas pressure, set to the rating plate value.
- Check burners sit in the locating slots, level front to rear and side to side.
- Clean the carry-over.
- Replace any deformed orifice or one not lined up with its burner.
- Watch several light-offs after, listen for the thump.
Applies to: GMES9, GCES9, AMES9, ACES9, VMES9, VCES9 (single stage, 92% and 96%)
More furnace guides
- Airflow lower than demanded, furnace runs on low stage when high stage is expected
- Alternate combustion air opening (upflow or horizontal)
- Alternate vent/flue location (upflow or horizontal left)
- Annual inspection checklist
- Auxiliary limit control (location and purpose)
- Auxiliary limit switch open (blower compartment)
Take it to the job
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Source: Goodman Service and Troubleshooting GMES9*/GCES9*/AMES9*/ACES9*/VMES9*/VCES9* (RS6612016r3) , S-312 Checking for Delayed Ignition p.44. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.