Glow-Worm Boiler F28 Fault Code: Causes & Fixes

The F28 fault code means your Glow-Worm boiler has tried to light but failed to detect a flame, so it locks out for safety. You are left without heating or hot water until the problem is cleared. 

The most common causes are a frozen or blocked condensate pipe, a gas supply interruption, a faulty ignition electrode, problems with the gas valve, and occasionally a blocked flue.

UK homeowners and landlords regularly see this code appear, especially during cold snaps. Some causes can be sorted quickly at home, while others need a Gas Safe engineer. 

Having boiler cover in place means you are never left facing unexpected repair bills when ignition faults arise, and it can also protect you from more costly issues that develop if the problem is left unresolved.

What Does the Glow-Worm Boiler F28 Fault Code Mean?

The Glow-Worm boiler F28 fault code means an ignition failure. The control board has attempted to light the burner several times but has not detected a stable flame within the safety time limit. After the failed attempts the boiler locks out and displays F28.

This is a protective measure. It stops unburnt gas from building up and protects the appliance. You will usually hear the boiler trying to fire, followed by silence and the F28 code on the display. A single reset may clear a temporary glitch, but the code will return until the underlying cause is fixed.

What Causes the Glow-Worm Boiler F28 Fault Code?

The F28 fault code is triggered when the boiler cannot establish a flame during the ignition sequence. The main causes are a frozen or blocked condensate pipe, gas supply problems, a worn or dirty ignition electrode, a faulty gas valve, and less often a blocked flue.

Frozen or Blocked Condensate Pipe

A frozen condensate pipe is the most frequent reason for the F28 code during UK winters. Condensing boilers produce water as a by-product of efficient combustion. This water drains away through a small plastic pipe that exits the property to an outside drain. When temperatures drop, the water can freeze inside the pipe and create a blockage. The boiler detects that condensate cannot escape and refuses to ignite as a safety measure.

How to Fix

1. Locate the external section of the white or grey plastic condensate pipe where it comes out of the wall.
2. Pour warm (not boiling) water slowly along the exposed length of the pipe. A watering can works well.
3. Wrap a warm damp cloth or hold a hot water bottle against any icy sections.
4. Listen for a gurgling sound that shows the ice has melted and the blockage has cleared.
5. Once the pipe is free, go inside and press and hold the reset button on your Glow-Worm boiler for a few seconds.
6. Check that the boiler restarts and the F28 code has cleared. If it returns, the pipe may need insulating or further attention.

Gas Supply Issues

If gas is not reaching the boiler, it simply cannot light. This can happen when a prepayment meter has run out of credit, the main isolation valve has been turned off, there is a local supply interruption, or the meter regulator is restricted.

How to Fix

1. Check that other gas appliances in the home, such as a hob or fire, are working.
2. If you have a prepayment meter, ensure it has sufficient credit.
3. Confirm the main gas isolation valve at the meter is fully open (handle in line with the pipe).
4. If no gas is available anywhere in the property, contact your gas supplier.
5. Once gas is restored, reset the boiler once. If the F28 code remains, a Gas Safe engineer should check the gas pressure at the boiler.

Faulty or Dirty Ignition Electrode

The ignition electrode creates the spark that lights the gas and also helps detect the flame. Over time it can become coated with carbon, misaligned, or worn. When the spark is weak or the flame cannot be sensed, the boiler fails to light and displays the F28 error code after several attempts.

How to Fix

1. Do not open the boiler casing yourself. The electrode sits inside the combustion chamber.
2. Call a Gas Safe registered engineer who will inspect, clean or replace the electrode as needed.
3. The engineer will also check the gap and alignment against manufacturer settings.
4. Once the electrode is working correctly, the boiler is reset and the F28 code should clear.

Faulty or Incorrectly Adjusted Gas Valve

The gas valve controls the precise amount of gas that reaches the burner. If it sticks, fails or is set incorrectly, too little or no gas arrives and the flame never establishes.

How to Fix

1. Confirm that other gas appliances are working so you know gas is present in the property.
2. Do not attempt to adjust or open the gas valve. This is a gas-safety critical component.
3. A Gas Safe engineer will test the valve operation, check the gas rate and inlet pressure, and either adjust or replace the valve.
4. After the work is complete the boiler is reset and the F28 code should disappear.

Blocked Flue

Debris in the flue can prevent the correct airflow needed for safe ignition. The control system detects the restriction and locks out with the F28 code.

How to Fix

1. From ground level, visually inspect the flue terminal for obvious blockages such as leaves or nesting material.
2. Clear any loose debris you can safely reach.
3. Reset the boiler once and observe whether the code returns.
4. If the blockage is internal or high up, arrange for a Gas Safe engineer to inspect and clear the flue properly. A flue guard can be fitted if birds are a recurring problem.

How to Prevent the Glow-Worm Boiler F28 Fault Code

Preventing the F28 fault code is largely about keeping the condensate system clear and the ignition components in good condition. A few simple habits make a real difference.

1. Insulate the external condensate pipe with purpose-made foam lagging before winter arrives. This is one of the most effective steps you can take.
2. Keep the area around the outdoor pipe free of leaves, snow and debris so water can drain freely.
3. Book an annual boiler service with a Gas Safe engineer. During the service the condensate trap is cleaned, the electrodes are checked and the gas valve is inspected.
4. Make sure the boiler pressure stays between 1 and 1.5 bar when the system is cold.
5. Fit a flue terminal guard if birds or leaves regularly collect around the outlet.
6. Consider a boiler cover plan that includes annual servicing and prioritised repairs. This keeps your Glow-Worm appliance in good condition and means any future F28 or other fault is dealt with quickly without unexpected costs.

Get Protection for Your Glow-Worm Boiler with Cover from PlusHeat

Ignition lockouts such as the Glow-Worm boiler F28 fault code can leave a home without heating at the worst possible moment. 

A boiler cover plan from PlusHeat gives you 24/7 access to Gas Safe engineers, parts and labour included, and an annual service that helps stop many of these issues before they start. 

Whether you are a homeowner or a landlord looking after tenants, cover means one less thing to worry about when the temperature drops.

FAQs

Can I keep resetting my Glow-Worm boiler when the F28 code appears?

Reset once after checking the condensate pipe or gas supply. Repeated resets without fixing the cause will not clear the problem and can put extra stress on components. If the code returns, stop and call a Gas Safe engineer.

Is the F28 code the same as F29 on Glow-Worm boilers?

They are closely related. F28 means the boiler failed to establish a flame during ignition attempts. F29 means a flame that was already burning has gone out during operation. Both can involve condensate problems, but the sequence is different.

How long does it typically take an engineer to fix an F28 fault?

Many cases involving a frozen or blocked condensate system are resolved in under an hour once the engineer arrives. Electrode cleaning or gas valve work can take longer and may require a return visit if parts need ordering.

Will a boiler cover plan cover the cost of an F28 repair?

Yes. PlusHeat boiler cover plans include parts and labour for covered faults such as those that trigger the F28 code, so you avoid paying the full call-out and repair cost yourself.

Does the F28 code mean I need a new boiler?

In the majority of cases, no. The code points to a specific ignition or drainage issue that can usually be repaired. Only if the boiler is very old or other major components have failed would replacement become the more cost-effective option. An engineer will advise you after diagnosis.