Boiler Not Igniting: Common Causes and Fixes

There's nothing like standing in a cold kitchen, jabbing the reset button on your boiler, and watching absolutely nothing happen. A boiler that won't ignite is one of the most common faults engineers get called out for, and it's rarely a mystery once you know where to look.

Before you assume the worst, it's worth working through the usual suspects. Most ignition failures come down to a handful of causes, some of which you can check yourself in five minutes.

Low water pressure

If your pressure gauge is reading below 1 bar, most boilers will refuse to fire up at all. This is by far the most common reason for a "no ignition" fault and the easiest to fix. Our pressure guide walks through how to safely repressurise your system using the filling loop.

If you're topping up pressure every few weeks, that's a separate problem worth investigating, often a slow leak somewhere in the system.

Ignition lead or electrode fault

Modern boilers use an electronic spark to light the gas, similar to a car's spark plug. Over time, the ignition lead or electrode can corrode, crack, or simply wear out. You'll usually hear the boiler trying to click and spark but failing to catch. This isn't a DIY fix, it needs a Gas Safe registered engineer to replace the part safely.

Gas supply issues

Sometimes it's not the boiler at all. Check whether other gas appliances in the house, a hob or gas fire, are working. If nothing gas-powered is firing up, you may have a supply issue rather than a boiler fault, and that's worth reporting to your gas transporter rather than waiting on an engineer.

Blocked condensate pipe

In cold weather, the condensate pipe (which carries away waste water from the boiler) can freeze and block, triggering a fault code and preventing ignition. This is especially common with combi boilers during winter cold snaps. Thawing the pipe with warm water, if you can safely access it, often solves this instantly. The Energy Saving Trust has useful general guidance on winter boiler care.

Faulty PCB or gas valve

If pressure, ignition components, and gas supply all check out fine, the fault may sit with the printed circuit board or gas valve. These are more involved repairs and, depending on the age of the boiler, can sometimes cost close to what you'd pay towards a replacement. If your boiler is over ten years old and racking up repeat call-outs, it's worth reading our signs you need a new boiler guide before sinking more money into fixes.

When to call an engineer

Any fault involving ignition, gas valves, or PCBs should be diagnosed by a Gas Safe registered engineer, both for safety and because guesswork on boiler electronics rarely ends well. You can check any engineer's registration on the Gas Safe Register before they start work.

Regular servicing catches a lot of these faults before they leave you without heating, and our guide on how often a boiler should be serviced explains the typical schedule.

If your boiler is constantly cutting out or the repair bills are stacking up, it might be more sensible to look at new boiler costs rather than keep patching an ageing system. Whatever the age of your boiler, if it won't ignite today, get a fixed price and we'll get an engineer out to sort it.