F28 Glow-worm
Glow-worm F28 Fault: Ignition Failure Fix
F28 on a Glow-worm is the ignition failure lockout — the same code, with the same meaning, as on its Vaillant group siblings: the boiler attempted to light, couldn't establish a flame, and shut down pending attention and a manual reset. Winter's leading cause is the frozen condensate pipe; the year-round list is the standard ignition rota.
What the F28 code means
The shared group control logic runs the standard sequence — fan proof, gas valve, spark, flame confirmation — and F28 records failure to establish the flame within its window. The value-badge positioning changes nothing here: the ignition interlock and its conservative lockout behaviour are identical to the premium siblings', and the code table transfers wholesale, which is why engineers fluent in Vaillant faults read Glow-worms at sight.
What you can safely do yourself
Work the outside-the-case list in order. One: in freezing conditions, thaw the external condensate pipe with warm water and retry — the classic winter cause of this code family. Two: verify gas is actually reaching the property — a working hob says supply is fine; a dead hob plus a meter error message says call your supplier, not a heating engineer. Three: check a prepayment meter's credit. Four: press reset once and let the boiler attempt a full ignition sequence.
What not to do: repeatedly hammer the reset button. Each attempt on a genuinely faulty burner or gas valve is the boiler protecting you by refusing; ten resets don't fix the cause, they just delay the call. And never investigate beyond the case — ignition components, gas valves and burners are legally and practically Gas Safe work.
What causes it
Seasonal cause first: the frozen condensate pipe, winter's universal ignition-stopper — and on value-range installs the condensate run is that bit more likely to be the short, unlagged, straight-out-the-wall version that freezes first. Otherwise: gas supply interruptions (hob and meter checks), ageing electrodes and leads, gas valve faults, flue anomalies. Cost-engineered ignition components age a little earlier under hard use than premium equivalents, which is the honest brand-specific note — and the annual service is where that ageing gets caught before the cold snap presents it.
When to call a Gas Safe engineer
Past the thaw and supply checks, F28 is Gas Safe territory: electrodes, leads, valves and flues. The group parts pipeline makes Glow-worm ignition repairs cheap and fast — routinely a single visit. Two things to report when booking: whether the hob works, and what the start attempt sounds like (clicking, brief fire, nothing). Between them they sort most F28s into their category before the engineer leaves base.
Carbon monoxide is odourless and colourless. Our CO safety guide covers the symptoms, where alarms belong and the emergency response.
Frequently asked questions
What does F28 mean on a Glow-worm boiler?
Ignition failure — the boiler couldn't establish a flame at start-up and locked out. The code and meaning are shared with Vaillant group-wide. Thaw the condensate pipe in freezing weather and check gas supply first.
Why does my Glow-worm get F28 every winter?
Almost certainly the condensate run freezing — commonly a short unlagged external pipe. Lagging it is the cheap permanent fix; re-routing or upsizing the bore handles stubborn cases. Ask for it with the callout.
Can I fix F28 myself?
The outside-the-case causes only: condensate thaw, meter credit, gas supply confirmation via the hob, then one reset. Ignition components and the gas path are legally and practically Gas Safe work.
Are Glow-worm ignition repairs expensive?
Among the cheaper in the market: group-shared parts are ubiquitous and the layouts familiar to every engineer. Most F28 fixes are modest single visits — the expensive version is only the one deferred through a winter of resets.
How much does fixing an ignition fault cost?
If it's condensate freezing: often nothing beyond the thaw, plus lagging the pipe to prevent repeats. Component-level fixes — electrodes, leads, sensing parts — typically land at the modest end of repair pricing once diagnosed.
Why does this fault always happen in winter?
Two reasons stack: frozen condensate pipes — winter's signature lockout cause — and the sheer workload increase, which exposes marginal ignition components that idled through summer. A pre-season service catches most of the second group early.
Fixing causes, not symptoms
The theme running through our guides holds here too. A repair that addresses why the fault happened — the pressure that keeps dropping, the sludge that keeps returning, the condensate pipe that freezes every January — is the one you don't repeat next winter. When you book through our network, say you want the cause addressed rather than the symptom silenced; it occasionally costs a little more on the day and reliably costs less across the years you'll own the system.