A gas burner should normally produce a mostly blue flame. A yellow or orange flame usually indicates incomplete combustion, meaning the gas is not burning efficiently and may be producing soot and potentially dangerous carbon monoxide.
Common causes include:
1. Insufficient Air Supply
The most common cause.
- Air intake vents or burner ports may be blocked.
- The air shutter may be incorrectly adjusted.
- Dust, grease, lint, or debris can restrict airflow.
Symptoms:
- Lazy, soft yellow flames.
- Soot deposits on cookware or surrounding surfaces.
- Reduced heating efficiency.
2. Dirty Burner Ports
Burner holes can become partially blocked by:
- Dirt
- Rust flakes
- Food debris (on catering equipment)
- Grease buildup
This prevents proper mixing of gas and air.
Symptoms:
- Uneven flame pattern.
- Some flame tips yellow while others remain blue.
- Flames lifting from only part of the burner.
3. Incorrect Gas Pressure
Gas pressure that is too high or too low can affect combustion.
Possible causes:
- Faulty regulator.
- Incorrect injector/orifice size.
- Supply pressure issues.
Symptoms:
- Excessively large yellow flames.
- Flame instability.
- Poor appliance performance.
4. Blocked Venturi or Mixing Tube
The venturi draws air into the gas stream before combustion.
If blocked by:
- Spider webs
- Insects
- Dust
- Debris
the burner receives insufficient oxygen.
This is particularly common in appliances that have been stored or left unused.
5. Wrong Gas Type
If an appliance designed for Natural Gas is supplied with LPG (or vice versa) without the correct injectors:
- Air/fuel ratio becomes incorrect.
- Yellow flames commonly occur.
- Excess carbon monoxide can be produced.
6. Contaminants in the Flame
Certain airborne contaminants can temporarily cause yellow colouring:
- Dust in the air.
- Cleaning chemicals.
- Sodium compounds (salt).
This usually creates bright yellow streaks but does not necessarily indicate a burner fault.
7. Faulty Burner Design or Damage
- Warped burners.
- Corroded burner heads.
- Damaged flame spreaders.
- Missing burner components.
These can disrupt the gas-air mixture and produce yellow flames.
When to Be Concerned
You should investigate immediately if you notice:
- Soot formation.
- Black deposits.
- Strong gas odour.
- Headaches or dizziness nearby.
- Flames that are predominantly yellow rather than blue.
These can indicate incomplete combustion and possible carbon monoxide production.
For Commercial Catering Equipment
If you're dealing with a commercial burner, oven, grill, or heated display unit, I would check in this order:
- Burner ports for blockage.
- Venturi/mixing tube for debris.
- Air shutter adjustment.
- Gas pressure at the appliance.
- Injector size and gas type compatibility.
A photo of the flame and burner assembly can often help identify the fault very quickly.