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Flame burns a few seconds then out
What is going on
Possible causes and checks for: flame burns a few seconds then out.
Likely causes
- Cad cell/stack switch mispositioned or faulty
- Excess air or air too cold
- Lean flame. Also flame failure general list: tank empty/not vented
- Clogged filter
- Ice/water/dirt in line
- Loose fitting (air)
- Loose wiring
- Motor off (reset)
- Bad fuel unit
- Pump losing prime
- Slipping coupling/pressure swing
- Clogged/damaged nozzle
- Bypass plug wrong
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Source: General HVAC service practice — verify per model. 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.