The Glow-worm boiler F28 fault code means your boiler has failed to ignite properly. It has tried to light several times without success and locked out as a safety measure. This leaves you without heating or hot water. Common triggers include problems with the gas supply, a frozen condensate pipe, blockages in the flue, or worn ignition parts.
If you live in the North West, Yorkshire or the Midlands and your Glow-worm is showing this code, the steps below will help you understand what is happening and what you can safely try before calling in a professional.
What Does the Glow-Worm Boiler F28 Fault Code Mean?
The F28 fault code means your Glow-worm boiler has been unable to establish a flame during start-up. Modern Glow-worm models (including many in the Energy range) attempt ignition a few times. When they detect no flame, they shut down and display F28 to protect the appliance and your home.
You may hear clicking as it tries to spark, but no heat or hot water follows. This is a safety lockout, not a random glitch. It points to an issue somewhere in the gas supply, ignition system or exhaust path.
What Causes the F28 Fault Code On Your Glow-Worm Boiler?
The F28 fault code on a Glow-worm boiler is almost always linked to ignition failure. Several everyday issues can stop the burner lighting reliably. Below we break down the most common causes and the practical steps to resolve them.
Gas Supply Problems or Low Gas Pressure
A lack of gas or insufficient pressure is one of the most frequent reasons a Glow-worm shows F28 error code. This can happen if your gas meter has run out of credit, the supply has been interrupted, air has entered the pipes, or the pressure at the boiler is simply too low for proper ignition.
Newer, more powerful boilers sometimes reveal that an older gas main cannot deliver enough flow. Cold weather can also freeze the regulator on the meter, restricting supply.
How to Fix
- Check whether other gas appliances in the house (hob, fire or cooker) are working. If none of them light, the problem is with the supply rather than the boiler.
- Look at your gas meter. If it is a prepayment meter, top it up and wait a few minutes.
- Once gas is confirmed, locate the reset button on your Glow-worm control panel (usually marked with a flame symbol and a line through it). Press and hold for three to five seconds, then release.
- Allow the boiler to attempt a restart and watch the display. If F28 clears and the boiler fires normally, monitor it for the next hour.
- If the code returns immediately or other appliances still have no gas, contact your gas supplier or a Gas Safe registered engineer. Do not keep resetting the boiler.
Frozen or Blocked Condensate Pipe
In colder months the plastic condensate pipe that runs outside from the boiler can freeze. Condensing boilers produce acidic water that drains away through this pipe. When ice blocks it, the boiler cannot vent properly and locks out with an F28 (or sometimes F29). This is extremely common across the North West, Yorkshire and the Midlands during hard frosts.
How to Fix
- Find the white plastic condensate pipe where it exits the wall near the boiler and runs to a drain.
- Feel along the external section for the frozen part (it will feel solid or show visible ice).
- Pour warm (not boiling) water from a kettle or jug slowly over the frozen section. A hot-water bottle wrapped around the pipe also works.
- Once the ice has melted and water can flow freely, return indoors and reset the boiler by holding the reset button for three to five seconds.
- After the boiler restarts, lag the external pipe with foam insulation to reduce the chance of it freezing again. If the pipe keeps freezing or you cannot locate the blockage, call a Gas Safe engineer.
Blocked Flue
The flue carries exhaust gases safely outside. Leaves, nests, debris or a damaged terminal can restrict the airflow. Without a clear path for the gases, the boiler detects an unsafe condition and refuses to ignite, displaying F28 code. This can also occur if the flue has come apart through age or movement.
How to Fix
- From outside, carefully inspect the flue terminal for obvious blockages such as leaves, bird nests or debris. Do not climb onto roofs or use ladders if you are unsure.
- Clear any loose material you can reach safely by hand or with a soft brush.
- Return indoors and reset the boiler.
- If the terminal looks damaged, missing its guard, or the code persists, stop and arrange a Gas Safe registered engineer. They will check the entire flue run and clear or replace any restricted sections.
Faulty Gas Valve
The gas valve controls the precise amount of gas reaching the burner. If it sticks, is incorrectly adjusted, or fails electrically, the burner receives too little or no gas and ignition fails. This is more common on boilers that have not been serviced regularly or are approaching the end of their typical 10–15 year lifespan.
How to Fix
- Confirm that other gas appliances are working so the supply itself is not the issue.
- Reset the boiler once and observe whether it attempts to light.
- If F28 returns, do not attempt further resets or any internal adjustments.
- Contact a Gas Safe registered engineer. They will test gas pressure at the valve, check the electrical connections and either adjust or replace the valve as needed. Valve work must only be carried out by a qualified professional.
Faulty Ignition Electrodes, Leads or Spark Generator
The spark generator, ignition electrodes and connecting leads create the spark that lights the gas. Over time these parts wear, corrode (especially in humid conditions) or become coated in debris. Without a reliable spark the boiler cannot establish a flame and locks out with F28 fault code. This is a frequent issue on Glow-worm models that are five to ten years old or older.
How to Fix
- Reset the boiler once after confirming gas supply is present.
- Listen carefully during the ignition attempt. A healthy system produces a clear series of clicks; silence or weak clicking can point to a spark problem.
- If the code reappears, switch the boiler off at the isolator and call a Gas Safe engineer.
- The engineer will inspect and clean or replace the electrodes, leads and spark generator, then retest the ignition sequence. These components are not DIY items because of the electrical and gas safety risks.
Debris in the Burner
Even small particles of dust, soot or corrosion can block the fine jets in the burner. When gas cannot flow evenly the flame fails to form and the boiler records an ignition fault. This often develops gradually on boilers that have missed annual services.
How to Fix
- Reset the boiler once to rule out a temporary glitch.
- If F28 returns, book a Gas Safe registered engineer.
- The engineer will isolate the gas, open the combustion chamber, clean the burner and jets thoroughly, check for any related wear, and then reassemble and test the appliance. Regular servicing helps prevent this build-up returning.
Faulty Printed Circuit Board (PCB)
The PCB is the boiler’s control brain. If it develops a fault it may misread sensors or fail to send the correct signals to the gas valve and ignition system, resulting in an F28 lockout. PCB problems are less common than gas or ignition issues but become more likely as a boiler ages past ten years.
How to Fix
- Carry out the basic gas-supply and reset checks listed earlier.
- If the code persists and other causes have been ruled out, contact a Gas Safe engineer.
- They will diagnose the board with specialist equipment. Replacement is sometimes required and can be one of the more expensive single repairs, which is why many homeowners in this situation start to weigh the cost against a full boiler replacement.
Throughout the North West, Yorkshire and the Midlands, Clever Energy Boilers installs modern, efficient boilers for homeowners and landlords who are tired of repeated fault codes. If your Glow-worm is becoming unreliable, a free, no-obligation quote can show you how straightforward a replacement can be.
When Persistent F28 Codes Point to a Bigger Decision
Repeated Glow-worm boiler F28 fault codes can quickly become expensive. Average boiler repairs in the UK sit around £300, and major components such as gas valves or PCBs cost more. Once a boiler is over ten to twelve years old, the chance of further faults rises and spare parts can become harder to source. Older boilers also tend to run less efficiently, adding roughly £200 a year to energy bills through wasted gas.
For many households the practical choice is to stop patching an ageing appliance and move to a new, reliable boiler with a long manufacturer guarantee. Clever Energy Boilers specialises in expert boiler installation across the North West, Yorkshire and the Midlands. We help both homeowners and landlords choose the right system, handle the full installation and leave you with dependable heating and hot water.
Request your free boiler quote today and find out how simple the switch can be.
Frequently Asked Questions
Can a Glow-worm F28 fault code clear on its own?
No. Once the boiler has locked out it will stay locked until the underlying cause is fixed and the unit is reset. Temporary power cuts or very brief supply interruptions occasionally clear after a reset, but the code almost always returns if the root problem remains.
Is it safe to keep resetting a Glow-worm showing F28?
Resetting once after checking the gas supply is reasonable. Repeated resets without fixing the cause can allow unburned gas to build up and place unnecessary stress on the components. If the code returns, stop resetting and call a Gas Safe engineer.
Does the F28 code appear on all Glow-worm models?
Yes. The F28 (sometimes shown as F.28) is used across the Glow-worm range, including the popular Energy models, to indicate unsuccessful ignition at start-up. The exact display may vary slightly by control panel style, but the meaning stays the same.
How long does a typical Glow-worm boiler last before major ignition faults become common?
Most UK gas boilers last between 10 and 15 years with regular servicing. After that point ignition components, valves and control boards wear more quickly, making codes such as F28 more frequent. Annual Gas Safe servicing is the best way to keep any Glow-worm running reliably for as long as possible.
Will a new boiler still show F28 if the gas supply is the real problem?
A brand-new boiler can still display an ignition fault if the gas pressure or pipework is inadequate. A competent installer will always check the gas supply during the survey and installation so that the new appliance receives the correct flow from day one.
