Boiler Ignition Fault: Why It Won’t Light (Next Steps)

When a boiler displays an ignition fault or flame failure message, it has been unable to light correctly or keep the burner alight. The boiler may lock out as a safety measure, leaving you without heating or hot water until the cause is identified and resolved.

Some basic checks can help you provide useful information to a heating engineer, but gas appliances should not be opened or repaired by homeowners. Here is what the fault may mean, what you can safely check and what a qualified engineer will inspect.

What an ignition fault or flame failure means

An ignition fault generally means the boiler has tried to start the burner but has not detected a successful ignition. A flame failure means the burner lit, or appeared to light, but the boiler then failed to detect a stable flame and shut itself down.

Modern boilers use sensors and control systems to confirm that gas is burning safely. If the expected signal is missing, the appliance will usually stop and show a fault code. The exact meaning of that code varies between manufacturers and models, so make a note of it before switching the boiler off.

Common causes of a boiler that will not light

A disrupted gas supply is one of the first things to consider. A meter issue, an interruption to the local supply or a partially closed isolation valve can prevent the boiler from receiving enough gas. If other gas appliances are also not working, contact your gas supplier or network operator rather than attempting to adjust gas controls.

The ignition electrode can become worn, dirty or damaged over time. This component creates the spark needed to light the burner, while a flame sensor confirms that combustion has taken place. A faulty sensor, poor electrical connection or damaged wiring can therefore cause repeated flame failure even when the gas supply is available.

• Gas supply interruption, meter problems or a valve issue

• Worn ignition electrode or faulty flame sensor

• Blocked condensate pipe or condensate drainage problem

• Fan or air pressure switch fault

• Printed circuit board or control fault

In colder weather, a frozen condensate pipe can stop the boiler from operating correctly and may lead to a lockout. Fan or air pressure switch problems can also prevent the boiler from proving that it has the correct airflow for safe combustion. In other cases, the issue may involve the printed circuit board, which controls ignition and monitors the appliance.

Safe checks to make before calling an engineer

Start by checking whether your hob or another gas appliance is working. If it is not, there may be a wider gas supply problem. Do not dismantle the boiler, remove its casing or try to clean internal components, as this can create serious safety risks and must be handled by a Gas Safe registered engineer.

Check that the boiler has electrical power and look at the display for a fault code. Confirm that the thermostat and programmer are switched on, set correctly and calling for heat. You can carry out a single reset only if the boiler manufacturer’s instructions allow it. If the fault returns, stop resetting the appliance and arrange professional help.

Safety first: act quickly if you smell gas

If you smell gas, suspect fumes or notice signs of unsafe combustion, turn off the gas supply at the meter if it is safe to do so, avoid using electrical switches and extinguish naked flames. Leave the property and call the National Gas Emergency Service on 0800 111 999 in Great Britain. Do not try to restart the boiler or investigate the fault yourself.

What a heating engineer will check

When an engineer arrives, they will first establish the symptoms and review any displayed fault code. They may check the gas supply, electrical power, thermostat demand and the boiler’s fault history before carrying out targeted component tests.

Professional boiler repairs should also include checks that cannot be safely completed by a homeowner. These may include inspecting flue integrity, taking combustion readings and testing the ignition electrode, flame sensor, fan, air pressure switch, condensate system and relevant control components. This helps identify the underlying problem rather than simply clearing the lockout.