BoilerFaultCodesYellow or orange boiler flame? Turn it off.
A healthy gas flame burns crisp blue. If your boiler's flame is yellow, orange, or "lazy" (floppy and smoky), that's a sign of incomplete combustion. Incomplete combustion produces carbon monoxide — which you cannot see, smell, or taste, and which can be fatal at surprisingly low concentrations.
Do this now
- 1. Turn the boiler off at the isolation switch or fused spur.
- 2. Open windows to ventilate the room.
- 3. Don't use the boiler, cooker, or fire until checked.
- 4. Call a Gas Safe engineer — say it's a yellow-flame issue so they prioritise.
- 5. If anyone feels dizzy, nauseous, or has a headache: leave the property and call 999. Those are CO poisoning symptoms.
National Gas Emergency: 0800 111 999 (free, 24/7)
Why does the flame turn yellow?
A blue flame means enough oxygen is mixing with the gas for complete combustion. Yellow flames appear when something is reducing oxygen supply or changing the air-to-gas ratio. Common causes:
- › Blocked burner or air intake: Dust, soot, or spider webs
- › Dirty heat exchanger: Soot build-up insulating the burner
- › Blocked flue: Exhaust gases recirculating
- › Incorrect gas pressure: Meter or regulator issue
- › Damaged burner components: Worn injector, cracked combustion chamber
Fit a CO alarm if you don't have one
A carbon monoxide alarm costs £15–£25 and should be fitted in every room with a gas appliance. They last 7–10 years and have a "test" button — test monthly.
Look for the EN 50291 standard and the British Standard Kitemark. Don't buy unbranded ones from marketplaces.
Signs of CO poisoning
Easily mistaken for flu, a hangover, or food poisoning. If symptoms ease when you leave the house and return when you come back, suspect CO:
- › Headache
- › Dizziness
- › Nausea
- › Tiredness / drowsy
- › Confusion
- › Shortness of breath
- › Chest pain
- › Loss of consciousness
If you suspect CO poisoning: get outside for fresh air immediately and call 999 or NHS 111.