Is the fan running at this time?
It sounds like a relay on the PCB is stuck
Ok, definitely sounds like the PCB then.
A link to the manual;
F1 is flame failure
F26 is flame after boiler has shut down.
The whole ignition sequence is controlled by the PCB - what is the auto control box you are referring to?
Ok, I see it page 31.
Some other boilers have this - like a Honeywell ignition control box.
This box controls the ignition of the boiler but not the fan or APS so if this was faulty it would fire without the fan having to run.
Have you swapped this out at all?
i can only guide you on here, normally I would say check power to the ignitor, but it is on the same PCB and pulling the power plug off will simply stop it working.
The ignition is controlled by this PCB only, perhaps you check local providers for a price and take it from there?