Ignition lockout on a boiler: what it means and what to do

What does ignition lockout mean on a boiler?

Ignition lockout means the boiler went to light its burner, did not detect a flame, and stopped itself. A gas boiler checks for a flame each time it fires. If the flame never forms, or the boiler cannot sense it, the control board shuts the gas off and locks out rather than keep trying. The boiler then shows a fault code or a warning light until it is reset.

So the lockout is not the fault. It is the boiler protecting you from unburned gas. The fault is whatever stopped the flame forming or being detected, and that is what needs finding.

Some boilers lock out before they ever light. Others light, lose the flame while running, and lock out when they cannot get it back. Vaillant, for example, uses separate codes for the two: F28 when no flame is detected during ignition, and F29 when the flame is lost during operation. The safe checks below are the same either way.

Each maker shows ignition lockout under its own code, and the table below lists the ones we have guides for. Your boiler's manual is the final word for your model.

An ignition lockout on its own is not a gas emergency. But if you can smell gas or your carbon monoxide alarm is sounding, whatever the boiler is showing, call the National Gas Emergency Service on 0800 111 999 straight away.

Ignition lockout codes by boiler brand

What causes a boiler to go into ignition lockout?

Anything that stops a flame forming, or stops the boiler sensing one, can cause a lockout. Some causes sit outside the boiler and are quick to rule out. Most sit inside it and are engineer work.

The common outside causes are a gas supply interruption and a frozen condensate pipe. A prepayment meter that has run out of credit, or a meter valve left partly off, starves the burner of gas. In cold weather, a frozen condensate pipe is a very common cause, because the boiler cannot run properly while that pipe is blocked.

Inside the boiler, the usual suspects are the ignition electrode, the flame sensing electrode, the gas valve, the fan, the flue, low gas pressure, the wiring and the control board. An engineer will typically check the gas supply, the flue, the ignition and flame-sensing electrodes, the gas valve, the wiring and the control board. All of those are Gas Safe registered engineer work.

The table below sets out what is likely behind the lockout, what you might notice, and who can safely deal with it.

Ignition lockout causes at a glance

What you can safely check yourself

These checks do not involve opening the boiler. Never remove the casing or touch the gas valve, fan or electrodes: gas work needs a Gas Safe registered engineer.

• Check the timer and thermostat are asking for heat. If the boiler shows no fault code and simply is not firing, this is often the reason.
• Check your gas supply. See whether the hob or another gas appliance works, and check the credit if you have a prepayment meter.
• Check the fused spur switch next to the boiler is on, so the boiler has power.
• Check the pressure gauge. If it is below the level your manual gives, top it up once, following the manual's steps.
• Reset the boiler once, using the reset button or method your manual gives. Do this once only.
• If the lockout comes back after that one reset, stop resetting and book an engineer.

Why does my boiler keep going into ignition lockout?

A reset clears the lockout, but it does not fix anything. If the boiler locks out again straight away, or runs for a while and then locks out again, the cause is still there. Resetting again and again only overrides a safety system that is doing its job.

A lockout that keeps returning usually points to a part inside the boiler: an electrode that is worn or out of position, a gas valve or fan fault, a flue problem or low gas pressure. None of those are safe to work on yourself. A Gas Safe registered engineer can test each one and find the actual cause, rather than guess from the code. You can check an engineer's registration on the Gas Safe Register.

How much does it cost to fix an ignition lockout?

It depends on the cause, so we do not quote a figure here. Our UK boiler repair cost statistics page gives typical ranges with named sources. If you book a one-off repair with us, it carries a £95 call-out fee, and one-off repair visits run Monday to Friday, 09:00 to 17:00.

Does boiler cover include ignition lockout faults?

Cover is for future breakdowns, so it will not fix a fault your boiler is showing today. For that, request a repair callback or book a one-off repair. A Smart Plan boiler module can then cover the next fault.

Smart Plan is a service plan, not insurance. It is modular, so you pick only the cover you want. Boiler and central heating cover includes parts and labour up to £500 per 12-month period if your boiler is under 7 years old, or up to £200 if it is 7 years or older. Repairs are carried out through a network of thousands of engineers we work with, and gas work is always done by a Gas Safe registered engineer. Cover-plan call-outs run Monday to Friday, 08:00 to 18:00, and we aim to get an engineer out to you within two working days.

A £95 call-out fee applies in defined cases. That includes the first 30 days of a new agreement, when cover still applies but the fee is charged. A 12-month agreement period begins once you use a service. There is a 14-day cooling-off period, which ends once a service is carried out.

Boiler locked out? Ask us to call you back.

Tell us what your boiler is doing and we will get back to you to arrange a Gas Safe registered engineer. One-off repair visits run Monday to Friday, 09:00 to 17:00, with a £95 call-out fee. Prefer to cover the next fault? Build your own boiler cover online. A service plan, not insurance. Questions? Call 0333 772 6247, Monday to Friday, 08:00 to 18:00.

Boiler ignition lockout FAQs

Helpful links

• Ideal L2 fault code: flame loss and ignition lockout
• Worcester Bosch EA / 227 fault
• Vaillant F28: ignition lockout
• Vaillant F29 fault code
• Glow-worm F1 fault code
• Baxi E133 fault code
• Alpha E01 fault code: ignition failure
• Viessmann F4 fault code: no flame signal
• Boiler not firing up? Safe checks first
• Boiler fault codes by brand
• Book a one-off boiler repair
• UK boiler repair cost statistics
• Boiler and central heating cover
• Check an engineer on the Gas Safe Register
• Vaillant: boiler fault codes