Glow-worm Energy Combi Problems — Faults & Fixes
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →If you smell gas, call 0800 111 999. Gas boiler repairs must be carried out by a Gas Safe registered engineer.
The Glow-worm Energy is a solid, no-nonsense combi boiler that keeps thousands of UK homes warm and supplied with hot water — but like any heating system, it can throw a fault code when something needs attention. Most problems are straightforward: a dip in water pressure, a frozen drain pipe in winter, or occasionally an ignition hiccup. The good news is that many faults can be spotted and fixed quickly, often without calling an engineer. This guide walks through the most common fault codes on the Energy range (18kW, 25kW, and 30kW models), what triggers them, and which ones you can safely tackle yourself. However, anything involving the gas supply, ignition electrode, or sensor replacement must be left to a Gas Safe registered engineer — it's both a legal requirement and your safety.
Not sure if this matches your problem?
Use our interactive tool — answer a few questions and get a personalised diagnosis.
Seeing an error code?
Look up your specific fault code in our full Glow Worm fault code database.
Most likely cause & what to check
The Glow-worm Energy combi (18kW, 25kW, and 30kW versions) is a popular budget-friendly boiler from the Vaillant Group. Because it shares its core components and fault code system with the Vaillant ecoTEC, Gas Safe engineers who know Vaillant will also be familiar with the Glow-worm Energy. Manuals at glow-worm.co.uk/support or call 0330 100 3461.
Fault code F22 (low water pressure — most common): repressurise to 1.2 bar using the filling loop under the boiler. Close both valves and press reset. If pressure keeps falling, there is a leak to find.
Fault code F28 (ignition failure): reset once. Check gas supply at other appliances. If F28 returns, a Gas Safe engineer should inspect the ignition electrode and gas valve. Because the Energy shares components with the Vaillant ecoTEC, parts are readily available.
Fault code F29 (flame loss — common in winter): in cold weather, check the condensate drain pipe outside the property. A frozen condensate pipe is the single most common cause of F29 in winter. The pipe exits through the wall and runs to a drain — pour warm (not boiling) water along its length to thaw. Once thawed, reset the boiler.
F75 (pressure sensor fault): less common on the Energy than on the ecoTEC Plus, but still occurs. A Gas Safe engineer can replace the pressure sensor.
The Glow-worm Energy is generally considered reliable for a budget boiler. It carries a 2-year parts and labour warranty — shorter than premium brands. For repair quotes, contact glow-worm.co.uk or any Gas Safe engineer.
Not confident doing this yourself?
Post the job and we'll match you with vetted local engineers. Free, no obligation.
🛠 Tools & materials you may need
Was this guide helpful?
Frequently asked questions
What does fault code F22 mean on a Glow-worm Energy boiler?
F22 signals low water pressure in the system, usually sitting below 1 bar when it should be around 1.2 bar. This is the most common fault and is almost always fixable by re-pressurising the boiler using the filling loop beneath it. If the pressure drops again within days, you have a leak somewhere in the pipework or radiators that needs finding.
Why does my boiler show F29 in winter and how do I fix it?
F29 (flame loss) in cold weather is almost always caused by a frozen condensate drain pipe running outside your property. The simple fix is to pour warm water along the pipe's length to thaw it, then reset the boiler. Once thawed, the boiler should fire up normally — prevention next year means lagging the pipe or ensuring it drains to a proper gulley.
My boiler keeps showing F28 — is it safe to use?
F28 is an ignition failure fault; the boiler will not fire and produce heat, so it cannot be used. A single reset is worth trying, but if it returns, you must call a Gas Safe engineer to inspect the ignition electrode and gas valve. Do not attempt this repair yourself as it involves gas components.
How often do Glow-worm Energy boilers need servicing?
Annual servicing is best practice for any gas boiler and keeps the warranty valid; Glow-worm recommends it in the manual. Regular servicing catches wear on the ignition electrode and other parts before they fail, and a clean burner burns gas more efficiently. Budget around £100–£150 for a full annual check with a Gas Safe engineer.