A boiler pilot light that keeps going out is a common frustration, but it is usually caused by a small number of specific faults. Understanding what these are can help you decide whether you can resolve the issue yourself or need to call a professional.
A boiler pilot light that keeps going out is most often due to a faulty thermocouple, which costs £60-£120 to replace by a Gas Safe engineer. A blocked pilot jet or low gas pressure are less common causes. Check the flame colour and call a professional for repairs.
- A failing thermocouple causes 70% of pilot light outages (Gas Safe Register 2026).
- Replace a faulty thermocouple for £60-£120 by a Gas Safe engineer.
- A yellow or orange pilot flame indicates a blocked jet or debris.
- Low gas pressure from the mains can also extinguish the pilot light.
- Repeated outages waste gas and increase bills (Energy Saving Trust 2026).
- A failing thermocouple is the most common reason a boiler pilot light keeps going out
- A blocked pilot jet or gas supply issue can also extinguish the flame
- A draft or air current near the boiler can blow the pilot light out
- Quick numbers typical costs and failure rates for pilot light issues
- You can safely relight the pilot light yourself, but only if you follow the boiler's instructions
- When you must call a Gas Safe registered engineer to fix a pilot light that keeps going out
- A faulty gas valve or control board can also cause the pilot to go out
The most frequent cause of a pilot light repeatedly extinguishing is a failing thermocouple. If the pilot light goes out and you cannot relight it, or it stays lit for only a few minutes, a faulty thermocouple is the likely culprit in around 70% of cases (Gas Safe Register, 2026).
A failing thermocouple is the most common reason a boiler pilot light keeps going out
The thermocouple is a small safety device positioned in the pilot flame. It generates a tiny electrical voltage when heated, which keeps a gas valve open. If the thermocouple fails, it cannot sense the flame, so it shuts off the gas supply even when the pilot is lit. This is the most common single reason a pilot light goes out and will not stay lit.
A faulty thermocouple is often the first component to fail in older boilers, especially those over 10 years old. The Energy Saving Trust notes that a pilot light that repeatedly goes out can waste gas and increase bills, as the boiler cycles on and off unnecessarily (Energy Saving Trust, 2026). Replacing a thermocouple is a straightforward job for a Gas Safe engineer, typically costing between £60 and £120.
A blocked pilot jet or gas supply issue can also extinguish the flame
Dirt, debris, or even a spider web inside the pilot jet can restrict the gas flow, causing a weak or unstable flame that blows out. A build-up of soot from incomplete combustion can also block the jet over time. If the pilot flame looks yellow or orange rather than a steady blue, this is a sign of a blockage.
Low gas pressure from the mains supply can also cause the pilot to go out, though this is less common and often linked to wider supply problems. You might notice other gas appliances in your home behaving erratically at the same time. If you suspect a gas supply issue, contact your gas supplier or the National Gas Emergency Service on 0800 111 999 (Gas Safe Register, 2026).
A draft or air current near the boiler can blow the pilot light out
A strong draft from an open door, window, or vent near the boiler can physically extinguish the pilot flame. This is more likely in boilers located in kitchens, utility rooms, or near external doors. The Energy Saving Trust advises checking for drafts as a simple first step before calling an engineer (Energy Saving Trust, 2026).
If you can feel a draft near the boiler, try closing doors or windows and see if the pilot stays lit. If it does, you may need to seal gaps around the boiler or consider repositioning a vent. However, never block a permanent air vent that is required for the boiler to operate safely.
Quick numbers typical costs and failure rates for pilot light issues
| Repair type | Average cost (2026) | Time to fix | Likely cause of pilot light out |
|---|---|---|---|
| Thermocouple replacement | £60 – £120 | 30 – 60 minutes | Most common cause |
| Pilot jet cleaning | £50 – £90 | 20 – 40 minutes | Blocked jet |
| Gas supply check | £80 – £150 | 30 – 60 minutes | Low gas pressure |
| Full boiler service | £80 – £120 | 45 – 90 minutes | Multiple possible causes |
Costs are based on 2026 data from the trades directory Checkatrade and the Gas Safe Register (Checkatrade, 2026). Prices vary by region and engineer, so always obtain a written quote before work begins.
You can safely relight the pilot light yourself, but only if you follow the boiler’s instructions
Most modern boilers have a simple relight procedure printed on the boiler casing or in the manual. The Gas Safe Register advises that you should never attempt to relight a pilot light if you smell gas or suspect a gas leak. If you smell gas, call the National Gas Emergency Service on 0800 111 999 immediately (Gas Safe Register, 2026).
A relight procedure typically involves turning the gas control knob to “pilot”, pressing it in, and pressing the ignition button. Hold the knob in for 20–30 seconds after the flame lights, then release. If the flame goes out, wait a few minutes before trying again. If it fails repeatedly, do not keep trying – call a Gas Safe engineer.
How to safely relight a gas boiler pilot light
When you must call a Gas Safe registered engineer to fix a pilot light that keeps going out
If the pilot light goes out repeatedly after relighting, or if the boiler fails to stay lit for more than a few minutes, you need a professional. A Gas Safe registered engineer can test the thermocouple, clean or replace the pilot jet, and check the gas pressure.
It is illegal in the UK for anyone other than a Gas Safe registered engineer to work on gas appliances. Working on gas without registration can result in fines, prosecution, or invalidating your home insurance. You can find a registered engineer on the Gas Safe Register website (Gas Safe Register, 2026).
A faulty gas valve or control board can also cause the pilot to go out
The gas valve controls the flow of gas to both the pilot and main burner. If it fails, the pilot may not receive enough gas to stay lit. An electronic control board on modern boilers can also develop a fault that cuts power to the ignition system.
These are more complex and expensive repairs, typically costing £150–£300, and require a Gas Safe engineer. If your boiler is more than 10 years old and requires a gas valve or control board repair, the cost may approach the value of a new boiler. The Energy Saving Trust suggests that if repair costs exceed 50% of a new boiler’s price, replacement is often more cost-effective (Energy Saving Trust, 2026).
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Frequently Asked Questions
The most common cause is a faulty thermocouple, which fails to keep the gas valve open. A blocked pilot jet or low gas pressure can also extinguish the flame. Gas Safe Register (2026) states thermocouple failure accounts for about 70% of cases.
Replacing a thermocouple costs between £60 and £120 when done by a Gas Safe engineer. If the pilot jet is blocked, cleaning or replacement may add £50-£100. Prices vary by region and boiler type.
No, you should not attempt to repair a gas boiler yourself. Only a Gas Safe registered engineer can legally work on gas appliances in the UK. DIY repairs risk gas leaks, carbon monoxide poisoning, or voiding your warranty.
A yellow or orange pilot flame indicates incomplete combustion, often due to a blocked pilot jet or debris. This can cause the flame to be unstable and go out. A healthy pilot flame should be steady and blue.
A thermocouple typically lasts 5-10 years in a well-maintained boiler. Older boilers over 10 years old are more prone to thermocouple failure. Regular servicing by a Gas Safe engineer can extend its lifespan.
