Home›Blog›Pilot light keeps going out
Boiler Pilot Light Keeps Going Out? Causes and How to Fix It
A pilot light that keeps going out usually points to a worn thermocouple, a dirty pilot jet or a draught — but first check whether your boiler even has a pilot light, because most UK boilers fitted since 2005 don't. Here's how to tell which you have, how to relight safely, what repairs cost in 2026, and when to call a Gas Safe engineer.
Quick answer
If your boiler keeps losing its pilot light, the most common cause is a worn or faulty thermocouple — the safety device that cuts the gas when it can't sense the flame — followed by a dirty pilot jet, a draught down the flue, or a failing gas valve. You can attempt to relight a true standing pilot yourself (knob to "pilot", depress, light, hold around 60 seconds, release), but stop after two failed attempts.
Before anything else, check whether you actually have a pilot light. The vast majority of UK boilers installed since April 2005 are condensing combi or system boilers with electronic ignition and no standing pilot to relight — so a "won't ignite" fault on a modern boiler is an ignition or lockout issue, not a pilot-light problem. All gas, burner, flue and gas-valve work must be done by a Gas Safe registered engineer. If you smell gas, call the National Gas Emergency line on 0800 111 999.
Quick answer: does your boiler even have a pilot light?
This is the single most important question, and almost every guide online skips it. A standing pilot light is a small gas flame that burns continuously to ignite the main burner on demand.
Standing pilots are found mainly on older boilers — typically those installed before around 2005, floor-standing models, and older back boilers behind a gas fire. If you have one of these, the relight steps below apply.
Most modern boilers do not have a pilot light at all. Since April 2005, almost every new gas boiler fitted in the UK has had to be a high-efficiency condensing model, and these use electronic ignition — a spark that lights the burner only when heat is needed. There is nothing to relight.
If you have a modern condensing combi or system boiler, you don't have a pilot light. When it "won't light", it's an ignition or lockout fault, not a pilot problem. See our guide to an electronic ignition fault that won't light and how to understand why your boiler goes into lockout instead.
Which do I have? A 30-second checklist
- You have a standing pilot if: the boiler is pre-2005, you can see a small permanent blue flame through a viewing window, there's a gas control knob with "Off / Pilot / On" positions, or it's a floor-standing or back boiler.
- You have electronic ignition (no pilot) if: the boiler is wall-mounted and post-2005, it has a digital display or fault-code screen, it makes a clicking/sparking sound before it fires, and there's a reset button rather than a gas knob.
Not sure of the install date? Check the service record, the Benchmark logbook, or the data badge inside the casing. A modern wall-mounted condensing boiler — such as a current Worcester Bosch Greenstar, Vaillant ecoTEC, Ideal Logic or Baxi 600-series — uses electronic ignition and has no standing pilot to relight.
What a pilot light is and how the thermocouple safety cut-off works
On a standing-pilot boiler, the pilot flame plays on the tip of a thermocouple — a thin metal probe that acts as a safety sensor.
When the tip is heated by the flame it generates a tiny electrical voltage (a few millivolts). That voltage holds the gas valve open, allowing gas to keep flowing to the pilot.
If the flame goes out, the tip cools, the voltage drops, and the gas valve closes within seconds. This stops raw gas escaping into your home.
So a pilot that won't stay lit is often the safety system doing exactly its job — not always a "fault" in the dangerous sense. The trick is working out why the flame keeps failing, and that diagnosis is a Gas Safe engineer's job.
Why your pilot light keeps going out — the 6 causes, ranked
In rough order of how often they're to blame:
1. Faulty or worn thermocouple
The most common culprit. Thermocouples are exposed to constant heat and typically weaken over several years of use.
A worn thermocouple stops generating enough voltage to hold the gas valve open, so the valve closes and the pilot dies — often a few seconds after you release the control knob.
2. Dirty or blocked pilot jet (orifice)
The pilot flame comes from a tiny orifice that can clog with dust, soot, or corrosion. A partly blocked jet gives a weak, small or yellow/orange flame that can't keep the thermocouple hot enough.
A yellow rather than crisp blue flame is your visual clue here — and a sign of incomplete combustion (see the flame-colour section below).
3. Draught or wind down the flue
A strong draught — from wind blowing down the flue, an open door near the boiler, or poor sealing — can simply blow the pilot out. This is most common in exposed or coastal locations and during storms.
4. Faulty gas valve, regulator or low gas pressure
If the gas valve or regulator is failing, or supply pressure is low, the pilot won't get a steady feed and keeps cutting out. This is a Gas Safe job — see the symptoms of a faulty gas valve.
5. Thermocouple misaligned or too far from the flame
If the thermocouple tip has been knocked out of position or sits too far from the flame, it won't heat enough to hold the valve open — even though the part itself is fine. An engineer can reposition it.
6. Flue, condensate or debris problems
A blocked or restricted flue, debris in the burner area, or (on newer hybrid setups) a condensate issue can disrupt combustion and destabilise the flame. These need professional diagnosis.
How to relight your pilot light safely (step-by-step)
These steps apply only to a true standing-pilot boiler, and only to the simple, owner-permitted relight action. If yours has electronic ignition, skip to the reset note below. If you're not confident, leave it to a Gas Safe engineer.
Manual relight
- Turn the gas control knob to "Off" and wait at least 3 minutes for any gas to clear. If you smell gas, stop now and call 0800 111 999.
- Turn the knob to "Pilot".
- Press and hold the knob down (this lets gas reach the pilot).
- Press the igniter button, or hold a long lit taper/match to the pilot, until the flame catches.
- Keep the knob held down for around 60 seconds so the thermocouple heats up.
- Slowly release. If the flame stays lit, turn the knob to "On". If it goes out, the thermocouple likely needs attention from an engineer.
The two-attempt rule. If the pilot won't stay lit after two tries, stop. Don't keep cycling gas — turn the boiler off and call a Gas Safe registered engineer. Never dismantle the pilot assembly, clean the jet, or touch the thermocouple yourself; that's gas work for a registered engineer only.
If you have automatic / electronic ignition
Do not try to light anything manually — there's no pilot to light, and you should never introduce a flame to a modern boiler. Instead, try a controlled reset: see how to reset your boiler safely. If it locks out again, it needs an engineer.
Blue vs yellow pilot flame — what the colour tells you
Flame colour is a fast, free diagnostic. A healthy gas flame burns clean blue.
| Flame appearance | What it means | What to do |
|---|---|---|
| Crisp, steady blue | Healthy, complete combustion | Normal — no action needed |
| Small or flickering blue | Weak gas feed, draught or dirty jet | Check for obvious draughts; have a Gas Safe engineer inspect the jet |
| Yellow / orange or "lazy" | Incomplete combustion — possible carbon monoxide risk | Turn off and call a Gas Safe engineer |
A yellow or orange flame should never be ignored. It signals incomplete combustion, which can produce carbon monoxide.
Carbon monoxide and gas safety
Most pilot outages are a safety system working correctly. But certain signs mean stop and get help.
- Yellow/orange flame, soot or staining around the boiler suggests incomplete combustion and a possible carbon monoxide risk from your boiler.
- Headaches, dizziness or nausea that ease when you leave the house can indicate CO. Fit an audible CO alarm near the boiler.
- A smell of gas: don't switch anything on or off, open windows, and call the National Gas Emergency line on 0800 111 999. See what to do if you can smell gas.
Never bypass, jam or "trick" the thermocouple to keep the gas flowing. That defeats the safety cut-off and can let unburnt gas into your home.
Pilot light and ignition repair costs in 2026
Prices below are indicative UK ranges for 2026 and exclude any standing call-out charge. Independent Gas Safe engineers typically charge around £60–£100 for a call-out, with emergency/out-of-hours rates higher; larger firms often charge £99+. Costs run higher in London and the South East.
| Job | Indicative cost (2026) |
|---|---|
| Relight / diagnose pilot | £30–£120 |
| Thermocouple repair / refit | £30–£120 |
| Thermocouple replacement | £120–£180 |
| Clean pilot orifice (jet) | £30–£120 |
| Replace pilot orifice | £40–£130 |
| Gas valve replacement | £200–£400 |
The thermocouple part itself is cheap (often £10–£20); most of the cost is the engineer's labour. For wider context see typical boiler repair costs in 2026. These figures were last checked in 2026 and vary by region and boiler — always confirm the price with your engineer on the day.
Does boiler cover or warranty pay for this?
A thermocouple, pilot jet or ignition fault is usually treated as a standard repair. Whether it's paid for depends on your situation:
- Manufacturer's warranty: repairs are typically covered while the boiler is in warranty — provided it's been serviced annually and registered, as most warranties require an unbroken service history.
- Boiler cover / breakdown plans: many cover boiler repairs including ignition and thermocouple faults, subject to the plan terms.
Two things to watch: pre-existing faults (a problem that started before you took out the plan) are normally excluded, and missing your annual service can void cover. Plans differ widely, so always read what's actually included before you buy.
Boiler cover and breakdown plans come in two distinct forms: FCA-regulated boiler insurance and unregulated service/care plans — they are not the same thing, and an unregulated service plan is not "insurance", so check exactly which you're buying. You can compare boiler cover for 2026 from a selected panel of providers we work with — this is not the whole market, and we don't compare every provider available. We may earn a commission if you buy through our links; this never affects the price you pay. Prices are indicative and were last checked in 2026 — always confirm the current price and terms on the provider's own website.
Should you repair or replace?
Here's the angle nobody else covers. If your boiler has a standing pilot, it's almost certainly 15–20+ years old — and the pilot itself is quietly costing you money.
A standing pilot burns continuously — typically in the region of 600 BTU/hour, or very roughly 4 therms of gas a month — wasted whether or not you need heating. Over a year that adds up to gas you can't use.
On top of that, an old non-condensing boiler is far less efficient than a modern A-rated one. The Energy Saving Trust estimates that replacing an old (G-rated) gas boiler with a new A-rated condensing model plus a thermostat and controls could save a typical semi-detached home around £320 a year on energy bills (roughly £130 in a flat and up to about £500 in a detached house). Your own saving depends on the size and efficiency of your home, so treat these as a guide rather than a promise.
So the maths often looks like this: a repeated thermocouple or valve repair on a 20-year-old boiler may cost anywhere from £120 to £400 and only buy you a little more time, while a replacement removes the wasted pilot gas and cuts running costs. If breakdowns are becoming a habit, weigh it up properly and get an independent quote — see whether to repair or replace your boiler.
How to stop it happening again
- Annual service by a Gas Safe engineer — catches a weak thermocouple, dirty jet or failing valve before it strands you.
- Draught-proof the boiler location — seal gaps and avoid strong cross-draughts that can blow a pilot out.
- Fit a flue wind-deflector / cowl if wind down the flue is the problem (an engineer can advise and fit one).
- Magnetic system filter and inhibitor — keep the system clean so debris doesn't disrupt the wider boiler.
When to call a Gas Safe engineer
These are the red lines — stop and get a professional in:
- You can smell gas — leave it off and call 0800 111 999.
- The flame is yellow or orange, or there's soot/staining.
- The boiler repeatedly locks out or the pilot won't stay lit after two attempts.
- You suspect a gas valve, PCB, flue or pressure issue — all sealed-circuit and gas work is engineer-only.
By law, only a Gas Safe registered engineer may work on the gas side of your boiler. You can find a Gas Safe registered engineer via the official register. This article is general information only — it is not gas-safety, engineering or financial advice, and it doesn't take account of your individual circumstances.
Is it dangerous if the pilot light goes out?
Usually not, in itself — when the pilot fails, the thermocouple safety cut-off shuts the gas valve so raw gas can't escape. The danger signs are a smell of gas, a yellow/orange flame, or soot around the boiler, which can indicate a leak or incomplete combustion and carbon monoxide. In those cases, don't relight it — turn it off and call a Gas Safe engineer, and dial 0800 111 999 if you smell gas.
Why does my pilot light keep going out?
The most common cause is a worn thermocouple that no longer holds the gas valve open. Other causes are a dirty or blocked pilot jet, a draught down the flue, a failing gas valve or low gas pressure, or the thermocouple sitting too far from the flame. If yours is a modern boiler with electronic ignition, it has no pilot at all and the fault is an ignition or lockout problem instead. Diagnosis and any gas-side repair must be done by a Gas Safe registered engineer.
Can I relight the pilot light myself?
On a true standing-pilot boiler, yes — the simple relight is an owner-permitted action: turn the knob to "Pilot", hold it down, light the flame, keep holding for about 60 seconds, then release. Stop after two failed attempts and call an engineer, and never dismantle or clean any part yourself. On a modern boiler with electronic ignition there's nothing to light — never introduce a flame; try a reset instead.
What does a yellow pilot flame mean?
A healthy flame is crisp blue. A yellow, orange or "lazy" flame means incomplete combustion, often from a dirty jet, and can produce carbon monoxide. Treat it as a warning: turn the boiler off and book a Gas Safe engineer.
How do I know if I have manual or automatic ignition?
Look for a gas control knob with "Off / Pilot / On" and a small permanent flame — that's a manual standing pilot, usually on pre-2005 or floor-standing boilers. A wall-mounted boiler with a digital display, a reset button and a clicking/sparking sound when it fires has automatic electronic ignition and no pilot light.
How much gas does a standing pilot light use?
A standing pilot burns continuously — typically around 600 BTU/hour for a single-flame pilot, or very roughly 4 therms a month — whether or not you're heating the home. It's one reason modern condensing boilers dropped the pilot in favour of on-demand electronic ignition.
Should I replace the boiler if the pilot keeps going out?
A standing pilot means an older boiler (often 15–20+ years), so weigh repeated repair bills against efficiency. The Energy Saving Trust estimates a new A-rated boiler with controls could save a typical semi-detached home around £320 a year versus an old G-rated model (figures vary by home), and it removes the wasted pilot gas. If breakdowns are frequent, replacement often makes more sense than another repair — but get an independent assessment first.
Compare boiler cover the easy way
Compare boiler & central heating cover from a selected panel of UK providers and find a plan that fits your boiler and budget. Information, not advice — we show a chosen panel, not the whole market.
Compare boiler coverThis article is general information, not financial or gas-safety advice. We compare a selected panel of providers, not the whole market, and may earn a commission if you buy through our links. Always have gas appliances checked and repaired by a Gas Safe registered engineer; in a gas emergency call 0800 111 999. Prices are indicative UK guides for 2026 — confirm current prices on the provider's own site.