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Flame conditions table
What is going on
Possible causes and checks for: flame conditions table.
Likely causes
- Yellow flame: lack of primary air → reset primary air
- Check for blockage. Lifting flame: gas velocity faster than burning speed → reduce gas input or primary air. Popping flame: flashback at shutoff → increase gas pressure
- Reduce primary air
- Reduce orifice size
- Check valve and burners. Floating flame (very dangerous, CO): incomplete combustion → check gas flow
- Flue
- Burners
- Secondary air
- Primary air. Flame rollout (very dangerous): blocked flue
- Poor draft
- Insufficient air
- Overfiring → same checks. Good flame = soft blue
- No yellow tipping/lifting
- No flashback/pop/float/rollout
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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.