Glow-worm boilers
Glow-worm is a British boiler brand. It’s part of the Vaillant Group, alongside Vaillant. You’ll find Glow-worm boilers in a lot of UK homes.
The current Glow-worm gas boilers come in three main ranges: Energy, Ultimate and Easicom. Each one comes in different sizes. You’ll see a number on the model name, such as 25 or 30. That’s the size in kW (kilowatts). Many older names are still on walls across the country, such as Betacom, Flexicom and Ultracom.
How Glow-worm boilers show a fault
Newer Glow-worm boilers show a fault as F, a full stop and a number, such as F.28. These are the same style of codes that Vaillant uses, and many have the same meaning.
Older Glow-worm models can use different codes. A code on an old Betacom may not mean the same as on a new Energy. So always check the user guide for your exact model. Glow-worm keeps its manuals online, and we link to them below.
Glow-worm says a reset can often clear a fault, or get the boiler going again for a while. If a fault keeps coming back, it needs an engineer to find the cause.
Frozen pipes and F.28
When it’s very cold, F.28 or F.29 often means the condensate pipe has frozen. Glow-worm says you might hear a bubbling or gurgling noise too. The pipe usually freezes at its most open point, such as the end near the drain or around a bend. Our guide explains how to thaw a frozen condensate pipe safely.
Low pressure and F.22
F.22 is the code for low water pressure. Glow-worm says the normal range is 1 to 1.5 bar. You can usually fix it yourself in a few minutes. See how to top up low boiler pressure. If you keep having to top it up, there may be a leak somewhere. That needs an engineer to find it.
Glow-worm gas boiler ranges
These are the gas boiler ranges on the Glow-worm website as of 21/10/2026.
- Energy
- Ultimate
- Easicom
Older Glow-worm ranges
You may still find these in homes. They are no longer sold new, but many are still working.
- Betacom
- Flexicom
- Ultracom
- Ultracom2
- Micron
- Hideaway
Common Glow-worm fault codes
Codes can differ between models and ages of boiler. Always check the user manual for your exact model.
| Code | What it means | What you can do |
|---|---|---|
F.20 | The safety cut-out has switched the boiler off. | Check the pressure and top up if needed. Make sure radiator valves are open and there's no air in the system. Then call your installer if it keeps happening. |
F.22 | Low water pressure in the system. | Top up to between 1 and 1.5 bar with the filling loop. |
F.28 | The boiler has failed to light. | Check your gas supply and prepayment credit. In cold weather, check the condensate pipe outside for ice. |
F.29 | The flame went out and the boiler failed to relight. | Do the same checks as for F.28, then reset once. If it comes back, call an engineer. |
F.32 | Fan fault. | This needs an engineer. Don't open the boiler case. |
F.75 | The pressure didn't change enough when the heating pump started. | Check the pressure gauge and top up if it's low. If the code stays, call an engineer. |
Glow-worm manuals
Glow-worm puts its user guides and installation manuals on its own website. You can find Glow-worm manuals here. You'll need your model name. The GC number helps too. Our guide shows you how to find your boiler's model and GC number.
Stay safe. You can reset a boiler, top up its pressure and thaw a frozen condensate pipe yourself. Anything inside the case is a job for a Gas Safe registered engineer.
If you smell gas, leave the building and call 0800 111 999.