24hxi Glow worm boiler failing to F1


Hi,
I have an 18 month old 24hxi Glow worm boiler configured with a Honeywell 3 port valve, Llandis control panel, Honeywell wall thermostat and Honeywell cylinder thermostat. The system is configured as the Honeywell Y plan, and can supply hot water only, heating only or hot water and heating combined. It is a conventional system, not a combi.
Whilst under warranty (Year 1) the system kept dropping to F1 (fail to ignite) at apparently random times. A Glow worm engineer called and told me that there had been a fault with some of these models due to some spade terminals being poorly fitted. He re-crimped the terminals and all seemed OK.
The fault recurred very occasionally after this, but not sufficient to justify a call-out.
The only change from standard that I have done since then is to change the 3 terminal(+earth) - (with accellerate) Honeywell wall stat to a two wire programmable stat. I jumpered a wire from the Live terminal to terminal 4 in the panel behind the system programmer as per Honeywell's instructions for upgrading a T6360 wall thermostat to a 2 wire programmable.
The system happily supplied HW throughout this summer, but when we started requiring HW+Heating combined a few random F1s started to appear. More recently we got an F4, and our installer called, struggled to find a solution, but after a call to Glow worm he flicked a switch near top left of boiler, and the F4 disappeared. The installer seemed to think that this was just a random fault.
All seemed fine until we started to leave the heating and HW on in the night, when we began to wake to a flashing F1 again.
I have replaced the 3 port valve, the wall thermostat, the cylinder thermostat with identical but new items in the hope that this would fix things, but the dreaded F1s continue.
I have swapped back the original wall stat and removed the link, but the same problem persists.
Today - a partial breakthrough. The systems fails to F1 when there is still a demand for heat (via the wall thermostat) but the cylinder stat decides the cylinder is up to temp and switches off.
The 3 port valve correctly positions for HW only, both HW and CH, AND CH only.
I guess that the night period with low consumption of hot water allows sufficient time for the H/W thermostat to cut out, thus causing the F1, but I have no knowledge of why this might happen and a way to resolve things.
The system is quite happy to run in Hw only mode or CH only mode, or combined mode until the cylinder stat switches off.
I really would appreciate some advice. The only good news is that with the boiler etc downstairs and the cylinder etc upstairs I have probably exercised sufficiently today to allow me to eat the entire turkey myself this year! :>))
Thanks!
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This boiler sounds like a turkey, it doesn't work as intended. I would tell Glow Worm and the supplier to either get it sorted or replace it, the choice is theirs. It is not as though it has worked properly for a number of years and then developed a fault, it seems to be congenitally faulty.
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