How to Fix a Glow-worm F29 Fault Code

A Glow-worm F29 fault means the boiler established a flame and then lost it during operation or failed to reignite. The boiler locks out as a safety measure. Common causes include an interrupted or insufficient gas supply, flue-gas recirculation or blockage, condensate problems, earthing/ignition issues or another internal fault.

Some checks are safe to carry out yourself. If the fault remains after these, you'll need a Gas Safe engineer to diagnose the problem.

What Does the Glow-worm F29 Fault Code Mean?

The F29 code indicates flame loss during operation. This is different from F28: F28 is an ignition failure before a stable flame is established, while F29 occurs after the flame has been established and is then lost or cannot be re-established.

What Causes a Glow-worm F29 Fault?

Gas supply interruption or gas-valve issue

An interrupted gas supply, insufficient gas pressure or a gas-valve problem can cause the flame to drop out. Internal gas-pressure and gas-valve checks must be carried out by a Gas Safe engineer.

Re-ignition, flame-proving or earthing issues

If the flame is lost, the boiler may fail to re-establish it because of an ignition-transformer, electrode, flame-proving, wiring or earthing issue. These are engineer diagnostic checks.

Frozen condensate pipe

During freezing weather, the external condensate pipe can freeze and block the drainage route. This causes the boiler to lock out with an F29 fault.

Flue-gas recirculation or airflow problem

Incorrect flue-gas recirculation or a blocked flue/air path can contribute to flame loss on ranges where Glow-worm lists this under F29. The flue should only be inspected or repaired by a qualified engineer.

Electrical faults

Wiring, ignition controls or electronics can also contribute to recurring F29 faults and require professional diagnosis.

What Should You Do First?

If your Glow-worm boiler shows an F29 fault:

• Check whether your gas supply is working.
• Look for a frozen condensate pipe during cold weather.
• Try resetting the boiler once any obvious issue has been resolved.

Avoid repeatedly resetting the boiler if the fault keeps returning. If you're seeing a different error, our guide to Glow-worm boiler fault codes explains what each code means and the checks you can safely make.

How to Fix a Glow-worm F29 Fault

Check the gas supply

Make sure your gas meter is on.

If you use a prepayment meter, confirm there's enough credit.

If other gas appliances are also not working, contact your gas supplier.

Check the condensate pipe

Locate the white plastic condensate pipe outside your property.

If it's frozen, thaw it carefully using warm — not boiling — water before resetting the boiler.

Reset the boiler

Press and hold the reset button for around 3 to 5 seconds, following your boiler manual.

If the F29 fault returns immediately, further investigation is needed.

Low gas pressure

Low gas pressure or a faulty gas valve should only be tested by a Gas Safe registered engineer.

Faulty components

Re-ignition, flame-proving, wiring, earthing or PCB components may require testing and replacement by a qualified engineer.

When to Call a Gas Safe Engineer

Call an engineer if:

• The fault returns after resetting.
• Your gas supply appears normal.
• The boiler cannot keep or re-establish a stable flame.
• You suspect a faulty gas valve, PCB or electrical component.

Gas and electrical repairs should never be attempted without the correct qualifications. If the fault won't clear or keeps returning, book a professional boiler repair in London with one of our Gas Safe engineers.

How to Prevent the F29 Fault Returning

Reduce the chance of future F29 faults by:

• Servicing your boiler every year.
• Insulating external condensate pipework.
• Keeping your gas supply active if you use a prepayment meter.
• Having recurring flame-loss or re-ignition problems checked early.

Need Help With a Glow-worm F29 Fault?

If your Glow-worm boiler still displays an F29 fault after these checks, arrange a professional inspection.

If you've checked the gas supply, condensate pipe and reset the boiler without success, book a Gas Safe engineer. We'll diagnose the fault, explain what's causing it and get your heating working again.