Ignition lockout on a boiler: codes and safe checks

Ignition lockout on a gas boiler means it has stopped because it hasn't successfully established or detected the required flame.

Your exact model and fault code determine what the error means and which checks are appropriate.

Follow the user manual before attempting a reset, and arrange a Gas Safe engineer to check the boiler if the problem continues.

If you smell gas or suspect carbon monoxide, stop troubleshooting and follow the emergency advice below.

This guide covers domestic mains-gas boilers. Oil-burner faults and LPG supply troubleshooting need different guidance.

When should you stop and seek emergency help?

A lockout message does not prove that the appliance is safe.

A gas smell, carbon monoxide alarm or suspected exposure takes priority over checking the display, meter or reset button.

If you smell gas

• Do not smoke, light matches or use naked flames.

• Do not turn electrical switches on or off, including the boiler's power switch.

• Open doors and windows if you can do so safely. Turn off the gas at the meter only if it is safe and you know how. Do not enter a cellar to reach the meter.

• Leave the building and call the appropriate gas emergency service from outside.

These precautions follow National Gas emergency guidance. Do not try another gas appliance to test the supply.

• England, Scotland and Wales: call 0800 111 999.

• Northern Ireland: call 0800 002 001.

• LPG: contact your gas supplier directly.

What does your boiler's fault code mean?

A fault code identifies a condition the boiler has detected, not necessarily a failed component.

Record the make, exact model and complete code or flashing-light pattern before attempting any permitted restart.

Use your paperwork, user manual or an externally accessible model label. You do not need to remove the casing to investigate.

A photograph of the display can help preserve the full message.

Selected model-specific examples, not a universal code dictionary

Technical references: Ideal Logic Combi2 User Guide, October 2023, UIN 237664 A01, section 1.9; Vaillant ecoTEC pro operating instructions 0020244996_01, Appendix B, and installation and maintenance instructions 0020244995_05, page 47; Baxi's technical error-code table for the Duo-tec Combi range. References checked on 18 October 2026.

Low water pressure is identified separately as F01 on the Ideal Logic Combi2 and F.22 on the Vaillant models above.

Do not treat these as interchangeable with ignition faults. Equally, cold radiators, a blank display or no demand from the heating controls do not by themselves establish ignition lockout.

For more on the Baxi example, read our Baxi E133 fault guide. Always apply your own model's instructions and the emergency precautions above.

What can you safely check yourself?

Use this alongside the emergency advice above. Checks and restart instructions depend on your exact boiler model.

Keep checks external and limited to tasks intended for users in your boiler's instructions. Gas Safe Register's guidance on gas-appliance work distinguishes these tasks from work affecting gas components or combustion.

Only use the checks below after eliminating emergency warning signs.

Opening a controls flap as the user manual permits is different from unscrewing or removing the boiler casing to investigate a fault.

Observations to make before arranging diagnosis

The boiler's water-pressure gauge measures pressure in the heating-water circuit, not gas pressure. Measuring gas pressure and investigating internal components are professional diagnostic tasks, not homeowner checks.

If the condensate pipe may be frozen

A condensate pipe carries water produced during boiler operation to a drain. Freezing can obstruct an external section and cause a shutdown, but a fault code alone does not confirm this.

Never use boiling water, climb to reach the pipe or put yourself at risk on icy ground. Water spilled during thawing can freeze and create a slip hazard.

If you cannot confidently identify and safely reach the pipe, leave it to an engineer. Once a frozen blockage has cleared, follow your boiler's user-manual restart procedure.

If it still fails, arrange help rather than continuing attempts. Our frozen condensate pipe guidance explains the cold-weather issue in more detail.

Should you reset a boiler in ignition lockout?

A reset may be appropriate if your exact user manual allows it, there are no emergency warning signs and you have completed the relevant permitted checks.

There is no universal button-hold time or reset sequence for every boiler.

For example, the Ideal Logic Combi2 guide instructs users to press its restart button, while the cited Vaillant ecoTEC pro operating instructions specify their own fault-clearance procedure.

Do not transfer instructions between models or treat a permitted attempt limit as a target.

A reset allows another operating attempt. It does not identify or repair an underlying fault. If the permitted restart fails, or the fault returns, stop further attempts and arrange diagnosis.

A boiler that runs briefly before locking out again still needs attention.

What can cause repeated ignition lockout?

Possible causes include supply conditions, ignition or flame-detection faults, drainage problems and electrical controls.

Manufacturer fault procedures, including the cited Vaillant F.28/F.29 and Baxi E133 guidance, consider several possibilities rather than identifying one part from the code.

• Gas-supply conditions: interrupted or inadequate supply can prevent successful ignition. Another appliance working does not rule out a boiler-specific supply problem.

• Ignition and flame detection: producing a flame and detecting it are different functions. Electrodes, ignition equipment or their connections may require investigation.

• Condensate or combustion routes: drainage restrictions and certain air-intake or flue problems can affect operation.

• Electrical controls: internal connections or control electronics may be involved, but the code alone does not justify replacing a circuit board.

These investigations belong to a suitably qualified Gas Safe registered engineer. Do not clean electrodes, test a gas valve, inspect internal wiring, clear a flue or adjust combustion settings yourself.

Clicking, brief operation or a fault returning after a reset can help describe the sequence.

None confirms a particular failed component. Give those observations to the engineer rather than buying parts by guesswork.

What should you tell the engineer?

Record what you have already observed. Do not operate other gas appliances or repeat resets to collect information.

Give the engineer a clear account of the fault and what you have already done. Prepare:

• The boiler make, exact model and full code or light pattern.

• When the problem began and whether heating, hot water or both are affected.

• Whether it fails immediately or runs before stopping.

• Any known gas interruption, meter message or freezing weather.

• Which manual-permitted checks or restart attempts you have made, and what happened.

• Any recent servicing, repairs or other work before the fault started.

The engineer can follow the model's diagnostic procedure before recommending a repair. Ask them to explain the confirmed cause, proposed work and any separate parts or return-visit costs.

Otherwise, our boiler fault diagnosis and repair callouts page explains the service and booking information. Do not assume that an unresolved fault is covered by a warranty without checking the applicable terms.

What does an ignition-lockout repair cost?

iHeat advertises boiler callouts from £89, including VAT. This covers attendance, diagnosis and repair work possible without replacement parts.

It is a starting callout price, not a guaranteed total price for fixing ignition lockout.

The callout remains chargeable for attendance and diagnosis even if the repair cannot be completed. Check the repair callout inclusions and exclusions before booking.

Base a repair-versus-replacement decision on the confirmed fault, full repair quotation, boiler condition, parts availability and any applicable cover.

How can you stop this from happening?

Gas Safe Register recommends having gas appliances checked annually by a registered engineer.

Follow your boiler manufacturer's servicing instructions, and ask the engineer to review any recurring cold-weather drainage problem. Maintenance is not a guarantee against every lockout.

If lockout is already recurring, arrange a GaSafe engineer to check over your boiler rather than waiting for the next routine service.