How to Fix Glow-worm F1 Fault Code (UK)
Glow-worm showing F1 — Low pressure. UK diagnosis, likely spare (filling loop) and step-by-step reset.
Glow-worm
What the code means
F1 on a Glow-worm indicates low pressure. The boiler locks out to protect the heat exchanger and, on gas faults, to comply with the Gas Safety (Installation and Use) Regulations. Always reset to confirm the code is live, not historical.
Likely spare
The most common fix is the filling loop. Check the exploded diagram against the GC number on the data plate before ordering — Glow-worm revised parts on Glow-worm units mid-production.
Fix procedure
Repressurise 1-1.5 bar.
Log the fault and reset. If the code returns within 24 hours, escalate to full electrical diagnosis with a manometer and multimeter.
Frequently asked questions
- Can I reset F1 myself?
- You can press the reset button up to 3 times. If F1 returns, the boiler needs a Gas Safe engineer — it is illegal to repair gas components without registration.
- Is the part covered under warranty?
- Glow-worm standard warranty is 2–10 years depending on model. Registered installations get the full term. Check the sticker inside the case.
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