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.
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.
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.
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.
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.
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.
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.
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.
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:
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.
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.
| 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.)
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.
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Compare boiler coverCommon 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.
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.
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.
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.
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.