My gas hob will not light — what can I safely check myself?

A gas burner that will not light is very often something sitting a few millimetres out of place or a port blocked by a boil-over, and those are things a household can put right in five minutes with the gas off. What it is never is an invitation to go further in. The boundary below is set by law, not by caution.

Safety

What you'll need

• Every burner control confirmed off, and the burner completely cold
• A dry cloth
• A pin, a paperclip or a soft brush for clearing ports (optional)
• Warm soapy water and a soft brush for washing caps and crowns (optional)

Step by step

1. Confirm the supply is actually on before anything else.Do other gas appliances work — a boiler, a gas oven? Is the meter's emergency control valve open? Are you on a prepayment meter that has run out of credit? A whole-hob failure is far more often supply than burner.
2. Turn everything off and let the burner cool.Every knob to off, and cold enough to handle comfortably. A gas burner holds heat in the cast iron support long after the flame is out.
3. Check the burner cap is seated flat and centred.Lift it and put it back squarely on the crown. Most caps have a locating spigot or a recess and only sit correctly one way. A cap even slightly off its seat gives a lifting, yellow or one-sided flame, or no light at all — and it is the most common single cause after a clean.
4. Look at the flame ports around the crown.The slots cut around the edge of the crown are the flames. A boil-over blocks some of them, and the signature is a gap in the ring of flame that appears in the same place every time. Clear them cold with a pin or a soft brush — never with anything that widens or deforms the slot.
5. Wash the cap and crown properly if they are greasy.Both lift off on nearly every domestic hob. Warm soapy water and a soft brush, then dry them completely before refitting. Dry means dry: a wet crown will not light and it will corrode.
6. Wipe the ignition electrode dry and clean.The ceramic-tipped pin beside the burner produces the spark. Wet or greasy, it clicks without sparking, or sparks weakly to the wrong place. A dry cloth, cold, with the hob isolated electrically if you can. Do not bend it, do not adjust its gap — that is engineer work.
7. Refit everything and test one burner at a time.Cap centred, crown seated, everything dry. If it lights and holds, you are done. If it lights only while you hold the knob in and dies when you release it, that is the flame supervision device and it is not an owner fix.
8. Stop here and call a Gas Safe registered engineer for anything else.No spark at all on any burner, a burner that lights and dies when the knob is released, a persistent yellow or orange flame, sooting on pans, a burner that lights with a bang, or any smell. All of these are engineer work and some are urgent.

Tips

• If the spark works on every burner but one will not light, the fault is that burner's cap, crown or port. If no burner sparks, it is the ignition unit or the supply to it, and that is not yours.
• A gas flame should be crisp blue with a small blue inner cone. Yellow or orange tips, or soot on the base of pans, means incomplete combustion — stop using it and get it checked, because incomplete combustion produces carbon monoxide.
• An audible-alarm carbon monoxide detector to BS EN 50291 belongs in any room with a gas appliance. It is inexpensive and it covers the failure mode you cannot smell.
• After a hob clean, always check every cap is back on its own burner. The caps for different burner sizes are often similar but not interchangeable.

Common mistakes

• Clearing ports with a drill bit or a knife — Widening or deforming a port changes the gas and air mixture at that flame permanently. A pin that fits the slot without forcing is the only appropriate tool.
• Refitting a wet crown or cap — It will not light reliably, and water in the burner base is exactly where corrosion starts. Everything comes back bone dry.
• Continuing to use a burner that lights with a bang or burns yellow — Both indicate a combustion problem. Yellow flames mean incomplete combustion and carbon monoxide, which has no smell and no warning.

If it doesn't work

Questions people ask