Glow-worm F.28 Fault Code: Ignition Unsuccessful Guide

The F.28 fault code on a Glow-worm boiler means the boiler has tried to ignite but failed — ignition was unsuccessful when starting up.

What the F.28 fault code means

F.28 is a start-up failure — the boiler attempted to light the burner but could not establish a flame. This is similar to the Vaillant F.28 code (Glow-worm is part of the Vaillant group and shares some fault code numbering).

Possible causes of the F.28 fault

• Gas supply off or pressure too low — The gas may not be reaching the boiler.
• Air in the gas line — Air bubbles can prevent ignition.
• Ignition system defective — The ignition transformer, cable, plug, or electrode may be faulty.
• Gas valve defective — The gas valve may not be opening.
• Condensate duct blocked — A blockage can prevent proper combustion.
• Incorrect earthing — Poor earthing can affect the flame detection system.

Can you fix it yourself?

1. Check that your gas supply is turned on — Make sure other gas appliances are working.

2. Check for a frozen condensate pipe — In cold weather, the condensate pipe outside can freeze and block.

3. Try resetting the boiler — After checking the above, try resetting.

If the fault persists, the cause could be low gas pressure, air in the gas line, or a faulty ignition system. This needs a Gas Safe registered engineer.

Need help with your Glow-worm boiler?

Sanju's Heating covers Newbury, Basingstoke and Reading. Call us on 01635 74 50 40 or book online at sanjusheating.co.uk/book

Check our full Glow-worm fault code guide for help with other Glow-worm error codes.