Glow Worm Flexicom Boiler Failing to Fire Up in the Morning

[Flexicom]

We have a Glow Worm Flexicom Boiler and on colder mornings it is intermittently failing to fire up.

It's set to come on at 6.20 but on particularly cold mornings it doesn't come on. When it fails it is usually showing an F43 error code, hit the reset button and it fires up fine. The boiler then works again all day, with central heating coming on for 2 hours at 12 pm, then again at 4.30 pm until 7 pm and hot water used during the day without issue.

Previously on the colder mornings, it used to need 3, 4 or 5+ resets to finally get going. However, after ruling out that it was the condensate pipe freezing but still figuring it was cold-related, putting a fan heater on next to the boiler and setting a timer for it to heat up the area where the boiler is for 30 minutes prior it firing up has caused it to work fine on less cold mornings, and only to require 1 reset on the even colder ones when it fails.

Any ideas what would cause this?

 

[Gasmk1]

F43 is a generic code which means it could be anything, that the boiler pcb is sensing a fault could be anyone of sensors to the pcb itself. It will need a good gas breakdown engineer to trace it, if you don't know one I would recommend a fixed price call out by glowworm