F1
Glow-worm F1, Low water pressure, system below 0.5 bar
MEDIUMRepressurise to 1.5 bar. Recurring F1 means a leak, book a trace, don't keep topping up.
Same-day repairs on every Glow-worm model, Energy, Ultimate, Betacom and older Micron ranges, by Gas Safe engineers who understand the Vaillant-group internals shared across the range. Common parts on the van, one-visit fixes wherever the parts allow.
Average reply under 10 minutes. No obligation.
Call 020 3000 0000Glow-worm is part of the Vaillant Group, which is why many of its faults and error codes look familiar, the internals share design DNA with Vaillant ecoTEC. Across London we see F1 low-pressure lockouts (usually a slow leak on the system, not the boiler itself), F4 flame-loss faults on ageing ignition electrodes, and F22 pressure switch or sensor issues on units that have never been properly serviced.
The upside is strong parts availability and long-lived heat exchangers on the Ultimate and Energy ranges. Combine a repair with a magnetic filter and an annual service and most Glow-worms will run cleanly for another decade.
Repressurise to 1.5 bar. Recurring F1 means a leak, book a trace, don't keep topping up.
Often ignition electrode wear or a gas supply issue. Engineer only.
Usually a failed NTC sensor. A single-visit fix if the diagnosis is confirmed on the phone.
Pressure switch or wiring. Sometimes clears with a proper repressurise; recurring means the switch itself.
Ignition electrodes, gas valve or PCB. Don't keep resetting, book an engineer.
Showing a different code? Call 020 3000 0000 and read it to us, we'll tell you what it means over the phone, free.
If your Glow-worm is over 12 years old and facing a major repair, we'll give you honest repair-vs-replace numbers on site, see our new boiler installation options.
Fixed quote before work begins, 12-month workmanship guarantee, genuine or manufacturer-approved parts.
"F1 every fortnight for six months. We traced a weeping TRV upstairs, fixed properly, no repeat callouts."
"F22 lockout. New pressure switch fitted from the van, same day fix."
"F28 ignition failure. Electrodes gapped and replaced, boiler happy again inside an hour."
Glow-worm-trained Gas Safe engineers across all 32 London boroughs, 24/7.