Guide · Gas system
Gas hob that will not light: what to check
If you can smell gas but the burner will not light, turn the knob off, open the window and wait at least a minute before trying again. The most common causes are wet or misplaced flame spreaders, a dirty igniter and no power reaching the ignition. If the burner goes out when you let go of the knob, you usually have not held it down long enough, or the thermocouple is dirty. Only the technician touches pipes, taps, nozzles and valves.
20 minutes Difficulty: EasyUpdated 25 October 2026
If you smell a strong gas odour, do not try to light anything: no switches and no flames. Open the windows, close the gas tap at the meter if you can do so safely, leave and call the distributor's gas emergency line or 112 from outside. Clean only with the burners off, cold and the knobs closed, and unplug the hob if you can reach the plug. Do not take apart or tighten pipes, taps, nozzles or valves.
What you need
- Soft brush
- Hot water and washing-up liquid
- Dry cloth
- Wooden toothpick
Step by step
Tap a step to mark it as done.
Gas comes out but the burner will not light
If you can hear the hiss or smell the gas and the spark is there but the flame does not start, gas and spark are not meeting. It happens with a flame spreader wet after cleaning, with holes blocked by burnt food, with a cap out of place or with an igniter covered in grease. These you can fix yourself with the burner cold.
If everything is clean and in place and the burner still will not light, the gas may be arriving poorly: a clogged nozzle, the hob tap opening too little, a nearly empty cylinder or a problem upstream. If the other burners also struggle, the problem is before the hob. In all these cases you call the technician.
Do not hold the knob open for a long time hoping it will eventually light. Do not bring matches or a lighter to a burner that has already let gas out for several seconds: first close it and let it ventilate.
No spark, or it clicks all the time
If no burner sparks, check the power: plug, switch and trip switch. If it is missing on one burner only, usually that burner's igniter is dirty or wet, or it is cracked or too far from the flame spreader.
Clicking that continues even with the flame lit, or without touching the knobs, often comes from damp: a spill or a clean with too much water reaches the switches under the knobs. Dry thoroughly, leave the hob off for a few hours and try again. If it continues, the inside has to be checked, where the spark generator and connections are: that is technician's work, with the plug out.
Goes out when you let go of the knob: the thermocouple
Modern hobs usually have a safety device: the thermocouple, heated by the flame, keeps the gas open, and when the flame goes out the passage closes. That is why you have to hold the knob down for a few seconds when lighting. If you let go straight away, the thermocouple is still cold and the burner goes out.
If it goes out even when held down for a long time, check that the flame touches the tip of the thermocouple: a crooked or dirty flame spreader moves it. Clean the tip and refit the parts properly. If the burner still will not stay lit, the thermocouple or valve has to be replaced by the technician.
Do not jam the knob down with weights or elastic bands and do not try to bypass the thermocouple. It is what closes the gas when a spill or a draught puts the flame out.
Yellow or uneven flame
A gas flame should be blue. If it is yellow or orange, the gas is burning with too little air: it makes soot and, when combustion is incomplete, produces carbon monoxide, as the Iren gas safety guide reminds us. Simple causes are dirty flame spreaders, holes blocked by food or detergent, and caps put on wrongly.
If after cleaning the flame stays yellow or makes noise, the possible causes are nozzles not suited to your gas, for example a hob set for LPG used with natural gas, or too little air in the room. The nozzles are changed and adjusted by the technician. The ventilation openings in the kitchen must never be closed or covered.
When to stop and call a technician
- You smell gas even with the knobs closed: follow the emergency procedure and call the emergency line
- With clean flame spreaders and igniter, the burner still will not light or keeps going out
- The flame stays yellow, makes soot or lifts off the burner
- A knob is stiff or turns freely, or the burner seems not to close fully
- Nozzles, thermocouple or spark generator need replacing, or the hob has to be converted from LPG to natural gas
Frequently asked questions
How many seconds do I hold the knob down?
Usually a few seconds after the flame lights is enough. Bosch says up to 10 seconds if the burner struggles to stay lit. The exact time is in your hob's manual.
Why won't the burner light after I washed it?
Almost always because the flame spreader or igniter is still damp, or because a part was refitted crooked. Dry everything, refit level and try again.
Can I clean the burner nozzle myself?
No. The nozzle is the small calibrated hole the gas comes out of and is part of the gas circuit. If you widen or damage it, the flame changes and the gas can come out wrongly. The technician cleans or replaces it.
Is a yellow flame on the hob dangerous?
It is a sign of combustion with too little air, which makes soot and can produce carbon monoxide. Clean the flame spreaders. If it stays yellow, stop using that burner and have it checked.
Who repairs a gas hob in Campania?
In Naples and the rest of Campania we do. The company is authorised for gas systems, letter E of DM 37/2008. We check the nozzles, thermocouples and connection, and we tell you the price beforehand.
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