Glow-worm boilers covered on this site
Glow-worm is a long-established British boiler brand and part of the Vaillant Group. Because the two brands share a lot of engineering, many Glow-worm fault codes carry the same number and broadly the same meaning as on a Vaillant ecoTEC. The ranges we are asked about most are:
- Energy: combi, system and regular boilers, including the Energy7 and the Energy Store combi with built-in hot water storage.
- Ultimate: the higher-specification range, including the Ultimate 3 combi, system and regular boilers.
- Betacom: compact combis such as the Betacom 4, common in flats and smaller homes.
Older ranges such as Easicom, Flexicom, Ultracom and Sustain use similar F codes, but details differ. Always check a code against the manual for your exact model.
How Glow-worm fault codes appear
On current models the code shows on the display as the letter F, a dot and two digits, for example F.22 or F.28. Most people search for it without the dot, which is how we list codes on this site. Glow-worm's operating manuals explain that fault codes take priority over everything else on the screen, and if more than one fault is active the codes take turns, each showing for about two seconds. Write down every code you see.
How to reset a Glow-worm boiler safely
The method depends on the model. On the Energy7, the manual says to press the reset button for about one second, after which the boiler makes another attempt to light. Other models use a different button or symbol, so check your own manual before pressing anything. On any model:
- Deal with the likely cause first, such as low pressure, no gas or a frozen condensate pipe.
- Press reset once and give the boiler a few minutes to try again.
- Stop after two or three attempts. Glow-worm's own manuals say to contact a competent person if a fault is still there after three tries, which in practice means a Gas Safe registered engineer.
Never remove the front casing to look for the problem. Everything behind it is a job for a qualified engineer.
Checking the pressure
Most recent Glow-worm boilers show the system pressure as a number on the display rather than on a separate dial, although some older boilers have a gauge underneath. The operating manuals for the Ultimate 3 and Betacom 4 recommend 1 to 1.5 bar with the system cold. When pressure falls too low you will see the F22 code, and our guide to topping up with the filling loop shows how to put it right. If the reading climbs close to 3 bar when the heating is hot, read our guide to boiler pressure that is too high.
Common winter faults
Glow-worm manuals make the point that the condensate pipe must always be clear. In a hard frost the section that runs outside can freeze, and the boiler then tends to lock out with an ignition or flame fault such as F28 or F29. Thawing the pipe with warm (not boiling) water is a safe job for a homeowner, and our frozen condensate pipe guide explains how.
Glow-worm fault codes we cover
- F22: low water pressure, usually fixed by topping up.
- F28: ignition failure on start-up, often a gas supply or condensate problem.
- F29: flame lost while the boiler is running.
- F75: pressure sensor or pump fault, mainly seen on the Energy range.
Our Vaillant fault code pages can also help, as the two brands share many codes.
When to call an engineer
If you smell gas, turn off the supply at the meter if it is safe to do so, open doors and windows, and call the National Gas Emergency Service on 0800 111 999. For anything beyond the basic checks above, or if a code keeps returning, book a Gas Safe registered engineer. A yearly service catches many faults early, and our boiler service cost guide explains what it typically costs.