Boiler pilot light gone out: how to relight it safely

Does your boiler actually have a pilot light?

A pilot light is a small, permanent gas flame that stays lit so the main burner can light from it whenever the heating or hot water calls. You find them on older boilers: floor-standing models in kitchens, back boilers behind a gas fire, and older wall-hung boilers, typically ones with a small viewing window where you can see a flame, a knob marked with off, pilot and on, and a push-button igniter that clicks.

Most boilers fitted in the last twenty years or so light electronically instead. There is no flame burning between uses, so there is nothing to relight. If your boiler has a digital display, a fault code or a reset button, follow our guide on how to reset a boiler rather than looking for a pilot.

Before you touch anything: the gas smell check

Stand near the boiler and notice whether you can smell gas. Mains gas has an added smell, often compared to rotten eggs, so that leaks can be noticed.

• If you smell gas, do not relight the pilot, do not use the igniter or any switches, and do not use a naked flame.
• Turn off the gas at the meter if you can reach it safely, and open doors and windows.
• Leave the property and call the National Gas Emergency Service on 0800 111 999, which is free and open at all hours.
• If a carbon monoxide alarm is sounding, treat it as an emergency in the same way, even if you cannot smell anything.

Carbon monoxide has no smell. A gas smell check does not tell you whether a boiler is burning safely, which is why a lazy yellow flame or soot marks matter even when the air smells normal.

How to relight a boiler pilot light

Every model is slightly different, and the instructions for yours are normally on a label inside the front panel or the lower door. Use those if you have them. The sequence below is the one most older boilers share, to help you make sense of them.

• Turn the gas control knob to off and wait. Manufacturers usually ask for a few minutes so that any unburnt gas can clear. Use the time your instructions give.
• Open the lower door or remove the small access cover that the instructions say you can open. Never remove sealed panels, the main casing or anything held on with screws that the user guide does not mention.
• Turn the knob to the pilot position and press it in. Keep it pressed.
• While holding it in, press the igniter button. You should hear a click and see a small flame appear through the viewing window. Some models need several presses.
• Once the flame is lit, keep the knob held in for the time stated, often around 20 to 30 seconds. This lets a safety sensor called the thermocouple warm up and hold the gas valve open.
• Release the knob slowly. If the flame stays lit, turn the knob to on and set the thermostat or timer to call for heat so the main burner lights.
• If the pilot goes out as soon as you let go, wait the stated time again before a second attempt. Do not keep trying for longer than the instructions allow.

Why a pilot light goes out

A single outage is common and not necessarily a fault. A pilot that goes out again and again is telling you something.

What colour should the pilot flame be?

A healthy pilot flame is crisp and mostly blue, and it plays steadily onto the thermocouple tip. A flame that is large, floppy, orange or yellow is a sign of incomplete combustion, which is how a gas appliance produces carbon monoxide.

If you see a yellow flame, soot around the viewing window, black marks on the casing, or you or others in the house have headaches, dizziness or nausea that ease when you go out, turn the boiler off and do not use it until it has been checked. Our guide to the signs of carbon monoxide at home covers what to look for.

The autumn switch-on problem

Many owners of older boilers turn the pilot off in the warm months, then find in late September or October that it will not relight or will not stay lit. A thermocouple or pilot assembly that has sat cold and unused for months is more likely to play up on the first try.

It is worth relighting and running the heating on a mild day before the first cold spell, so any fault shows up while it is an inconvenience rather than an emergency. If the boiler has not been serviced in the last year, book that at the same time. An engineer can clean the pilot jet, check the thermocouple and test the flue while the boiler is out of use.

When to stop and call an engineer

Relighting from the user controls is fine. Anything beyond that is gas work and, by law, it must be done by a Gas Safe registered engineer. Stop and call if:

• The pilot will not light after two or three attempts following the instructions.
• It lights but goes out as soon as you release the knob.
• It keeps going out every few days, or on every windy day.
• The flame is yellow or orange, or there are soot or scorch marks.
• The boiler lights with a bang or a loud whoosh.
• You would need to remove any panel the user guide does not tell you to open.

Repair it or replace the boiler?

A thermocouple or pilot assembly is usually a modest repair where parts are still available. On many older boilers, though, parts are getting harder to find, and a boiler old enough to have a permanent pilot is also burning gas all year just to keep that flame going.

If the boiler has had several faults in a short time, parts are hard to get, or you are already thinking about efficiency, it is worth weighing up a repair against a replacement. Our guide on whether to repair or replace a boiler sets out how to make that decision.

Getting it looked at

Loyal Plumbers runs 10 vans across London and everywhere inside the M25, 24 hours a day, and all gas work is carried out by Gas Safe registered engineers. Our call-out charge is £60.

When you get in touch, tell us the boiler make and rough age, what happens when you try to relight it, and whether the flame looks blue or yellow. If you can smell gas, call the National Gas Emergency Service first and leave the property. Once they have made the supply safe, we can carry out the repair.