Boiler Ignition Fault: Why It Won't Light
An ignition fault means your boiler is trying to fire but the burner won't light — so you get no heating and no hot water. Some causes are simple things you can safely check; others sit behind the casing and need a Gas Safe registered engineer. Here's how to tell them apart.
Quick answer
A boiler ignition fault means the boiler is trying to fire but the burner won't light, so you get no heating and no hot water.
Safely check the easy causes first — that gas is reaching other appliances and the meter is in credit, that pressure reads about 1–1.5 bar (top up via the filling loop if low), and that an external condensate pipe hasn't frozen in winter — then press the front-panel reset once.
If it still won't light or it locks out again, stop resetting and call a Gas Safe registered engineer, as the cause is usually an electrode, the gas valve or a blocked flue.
When a combi, system or heat-only boiler has an ignition fault, the sequence is always the same: you ask it for heat, the fan spins up, the boiler attempts to light the burner — and nothing catches. After a few failed attempts it stops trying and usually shows a fault code or a red light.
That deliberate shut-down is the boiler protecting you from releasing unburnt gas. The good news is that several of the most common causes are perfectly safe for a homeowner to check in a couple of minutes. The rest are firmly engineer territory, and this guide draws a clear line between the two.
What an ignition fault actually means
Ignition failure is simply the boiler failing to establish a flame when it starts up. Most boilers make two or three attempts; if no flame is detected, they go into a safe shut-down (often called a lockout) and display a code.
Because there are several reasons a flame might not light, the same "won't light" symptom can have very different causes — some trivial, some serious. The job is to rule out the easy, safe ones first.
The safe things to check first
Work through these before you touch the reset button. None of them involves the gas, the flue or removing the casing, so they're all fine for a homeowner.
Is the gas actually getting through?
No gas means no flame. Check whether your other gas appliances work — does the gas hob light? If nothing gas-powered is working, the issue is the supply, not the boiler. If you're on a prepayment meter, check you haven't run out of credit. Also make sure the gas isn't switched off at the meter.
If the whole supply is off and you don't know why, or you suspect a wider problem, call your supplier rather than forcing the boiler.
Check the pressure gauge
Low water pressure can stop a boiler firing. Look at the gauge on the front: cold, it should read roughly 1 to 1.5 bar, rising towards 2 bar when hot.
If the needle sits below about 1 bar, often in a red zone, top it up via the filling loop — open the valve(s) on the silver braided hose slowly until the gauge reaches about 1.2–1.5 bar, then close it firmly. Our low boiler pressure guide covers it step by step.
If pressure keeps dropping, you have a leak or a failing part, which needs an engineer.
Check for a frozen condensate pipe (winter)
If the boiler stopped lighting during a cold snap — perhaps with a gurgling sound — suspect a frozen condensate pipe, the plastic drain that carries waste water outside.
Thawing the exposed external section is safe: pour warm (not boiling) water along the outside pipe, focusing on bends and the open end, then reset once. See our frozen condensate pipe guide. If the frozen part is inside a wall or out of reach, call an engineer.
Reset the boiler — once
A single front-panel reset is a normal homeowner action and won't harm anything. Hold the reset button for the few seconds your manual specifies and let the boiler run through its ignition sequence.
If it lights and stays running, the fault was a one-off — a brief gas dip or a single failed light-up — and you're done. If you're unsure where the reset button is, our how to reset your boiler guide covers the common brands.
When it's a Gas Safe engineer job
If the boiler still won't light after your safe checks and a single reset — or it lights and then locks out again — stop. Do not keep pressing reset. A repeated ignition lockout means a genuine fault that needs diagnosing, and the likely culprits all sit behind the casing or involve the gas and combustion circuit:
- Ignition or flame-sensing electrodes — worn, dirty, cracked or wrongly gapped, so the spark fails or the flame isn't detected.
- The gas valve — not opening correctly to deliver gas to the burner.
- A blocked or restricted flue — preventing safe combustion.
- A faulty fan, ignition lead or PCB controlling the start-up sequence.
Every one of those is strictly for a Gas Safe registered engineer. Never remove the boiler casing, and never touch the gas valve, gas pipework, the flue, the burner or the sealed combustion circuit yourself.
Repeatedly resetting a boiler that keeps failing to light can be unsafe — you're asking it to fire despite a fault it has already judged dangerous — and it won't fix anything.
Reading the fault code
Most boilers show an ignition fault as a specific code, and the meaning varies by brand. A few we've covered in detail: Vaillant F28 (ignition/gas supply failure on startup), Ideal L2 (ignition lockout, flame not detected) and Baxi E1 (no-ignition / flame-failure lockout).
Write down the exact code before you call an engineer — it speeds up diagnosis and helps them bring the right parts. Be wary of older online guides: some list the wrong meaning, so always check the code against your boiler's own manual or a current source.
Homeowner-safe vs engineer-only — at a glance
| Safe for you | Gas Safe engineer only |
|---|---|
| Checking other gas appliances and meter credit | Ignition / flame-sensing electrodes |
| Reading the pressure gauge and fault code | The gas valve and gas pipework |
| Topping up pressure via the filling loop | A blocked or restricted flue |
| Thawing an external condensate pipe | Anything behind the boiler casing |
| One front-panel reset | Repeated ignition lockouts, fan, PCB |
Always use an engineer listed on the Gas Safe Register and check their ID card before any work starts. (CORGI stopped being the UK gas registration body in 2009, when Gas Safe took over.)
Where boiler cover fits in
A one-off ignition fault you clear yourself costs nothing. But a failed gas valve, ignition electrode or fan can mean a call-out fee plus a pricey part — easily a few hundred pounds in one go.
That's the thinking behind boiler cover: a monthly plan that bundles repairs, parts and labour, and usually an annual service, so a sudden breakdown doesn't land as one large bill.
If you're weighing it up, our honest take is in is boiler cover worth it?, and you can compare what's included at different price points in our best boiler cover and cheap boiler cover guides.
Use our tool to compare boiler cover prices and find a plan that fits your boiler and your budget.
Boiler refusing to light?
Compare boiler cover plans with repairs, parts, labour and an annual service from a panel of UK providers — see exactly what each one includes and what you'd pay each month.
Compare boiler coverFrequently asked questions
Why won't my boiler ignite?
Common causes are no or low gas (check your hob and meter credit), low water pressure, or a frozen condensate pipe in winter — all of which you can check safely. If those are fine and it still won't light, the cause is usually an ignition electrode, the gas valve or a blocked flue, which need a Gas Safe registered engineer.
Can I fix an ignition fault myself?
You can safely check the gas supply and meter credit, top up pressure via the filling loop, thaw an exposed external condensate pipe and reset the boiler once. You must not touch the gas valve, electrodes, burner or flue, or remove the casing — those are engineer-only jobs.
Is it safe to keep resetting a boiler that won't light?
No. One reset is fine, but repeatedly resetting a boiler that keeps failing to light can be unsafe and won't fix the underlying fault. A repeated ignition lockout needs diagnosing by a Gas Safe registered engineer.
Why does my boiler only fail to light in cold weather?
That strongly points to a frozen condensate pipe. In freezing temperatures the external drain ices up, the condensate backs up, and the boiler shuts down. Thawing the exposed outside section with warm water and resetting once usually clears it — see our frozen condensate pipe guide.
Will boiler cover pay to fix an ignition fault?
Most plans cover breakdown repairs including parts and labour for faults that cause a boiler not to light — such as a failed gas valve, ignition electrode or fan — subject to the policy terms, limits and any excess. Always check the specific plan's inclusions and exclusions before buying.