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Yellow Or Orange Flame On The Hob
A gas hob burner that should burn crisp blue is burning yellow — a classic sign of incomplete combustion.
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What's happening?
A gas burner mixes gas with air before it lights. Get the mix right and it burns hot and blue with a sharp cone. Starve it of air and the flame turns lazy, yellow or orange, burns cooler, and leaves soot behind — and incomplete combustion is exactly the condition that produces carbon monoxide. HSE lists yellow or orange flames, soot or yellow-brown staining, pilot lights that keep blowing out, and increased condensation on windows as the visible signs that an appliance is not burning properly. The one exception is a decorative fuel-effect fire or a flueless appliance designed to show a yellow flame; a hob burner is not one of those.
What usually causes it?
- Burner ports blocked by spilt food, boil-over residue or cleaning product
- A burner cap sitting slightly off its crown after cleaning, distorting the flame pattern
- The air shutter or aeration setting knocked out of adjustment during a move or a repair
- An LPG appliance running on natural gas, or the reverse, because the conversion jets were never changed
- Injectors partially blocked with debris carried through the pipework after building work
- A room short of air, so the burner cannot draw enough for the gas rate — common in tightly sealed kitchens with the extractor on full
- Low gas pressure at the appliance from a partly closed valve or an undersized supply pipe
Is it dangerous?
It is a warning sign, so treat it as high. A hob is flueless, which means everything it burns goes into the room, and a burner producing carbon monoxide has nowhere to send it. Sooting also means unburnt carbon is landing on pans, worktops and the extractor. If the flame is yellow and anyone has been feeling headachy, drowsy or sick in the kitchen, stop using the hob and follow the carbon monoxide steps rather than trying to adjust the burner.
Can I fix it myself?
You may clean, and that is the limit. Let the hob cool, lift off the pan support, burner cap and crown, and wash off spilt food and grease. Clear the small flame ports with a soft brush — not a pin, which can enlarge them. Refit the cap so it seats squarely on the crown, and relight. If the flame comes back crisp and blue on every burner, that was it. Never open up the appliance, change an injector, or adjust an air shutter yourself: that is gas work, and under the Gas Safety (Installation and Use) Regulations only a Gas Safe registered person may do it.
When should you call a gas engineer?
If the flame stays yellow after cleaning, if more than one burner is affected, or if there is soot or staining anywhere, book a Gas Safe registered engineer. Call the same day if a CO alarm has ever sounded or anyone gets symptoms in the kitchen. Also call if the appliance has recently been moved, refitted, or run on bottled gas at any point — the wrong injectors will do exactly this.
What will the gas engineer actually do?
- Check the appliance is on the correct gas and that the injectors match it
- Read the working and standing gas pressure at the appliance test point against the data plate
- Strip and clean the burners, crowns and injectors, and reset the aeration where the design allows it
- Take an ambient CO reading in the room while the hob runs at full rate
- Assess the kitchen's ventilation and any extractor that could be depressurising the room
- Recommission the hob, confirm a clean blue flame on every burner, and record the readings
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