Recurring ignition fault (F.28 error) on new Vaillant Glow-Worm Boiler - Advice needed
Hello,
Has anyone else experienced recurring ignition faults with a Glow-Worm boiler? What was the solution? I have included as much information as possible below.
New boiler (Glow-Worm Ultimate3 30kW) installed in December, 2025 by a previously used, trusted Gas Safe Engineer. The boiler is in the loft. The condensate pipe was identified as being totally inadequate and not to regulation but the Gas Engineer did not replace it because of time constraints (the install was squeezed in the week before Christmas), which I was OK with. We have a toddler and I just wanted the old, broken boiler replaced before Christmas.
Boiler under a 10 year warranty from Vaillant.
(The condensate pipe was as bad as it gets. Total run length about 5-6 metres. 22 mm OD pipe. Various twists and turns and even a couple of short horizontal sections, one of which was almost going uphill. You don't have to be a Gas Engineer to see it was prone to freezing or backing up).
January 2026: Condensate pipe froze outside in the cold weather, causing F.28 ignition fault error. Boiler working again after defrosting and reset.
February 2026: F.28 error again. No obvious leaks, drop in pressure or cold weather causing freezing. Boiler working again after a reset.
Glow-Worm Engineer called out. Couldn't identify any issues with the boiler but said the condensate pipe needed replacing. I already knew this but life with a Toddler means these things don't get booked in. Glow-Worm Engineer replaced an electrode so that I would not get charged under the warranty scheme for a non-boiler component being the problem.
February 2026: Condensate pipe replaced by Gas Safe Engineer. Entire length of pipe is now 32 mm OD. Entire length of pipe is lagged with waterproof insulation. Total run length is now as short as reasonably possible, probably 2.5 m internal and 1 m external. The pipe terminates into the soil stack with a pipe boss connector, and has minimal changes of direction. There is a short horizontal section at the end going into the soil stack.
March 2026 - May 2026: Several more F.28 errors, once every fortnight I'd say. Each time they have been fixed by a reset. On one occasion the resting pressure had dropped to 0.9 bar but no obvious leaks and otherwise the pressure is maintained OK. I topped it up to ~ 1.4 bar.
Glow-Worm Engineer called out in March. Explained everything. He was more thorough that the Engineer who came out in February 2026. He couldn't identify anything wrong with the boiler after what seemed like a very thorough examination for 40 minutes, but he did notice excess grease from the installers etc - which he removed - and did replace the fan if I recall correctly as it can be a likely culprit. Despite his work, we've had more errors since.
What is going on? Is the boiler itself just faulty? Does the circuit board need replaced? Yes, I have 10 years of free Glow-Worm repairs but I just want it to work without error rather than call an Engineer out every month.
Thank you in advance.