Boiler not firing up, showing error code, help please

Hi
I have a Glow-worm boiler 60ff. It was working absolutely fine until last week. The PCB had a lighting sequence, where reset LED1 was flashing fast and the burner LED2 was flashing slow. So we gathered it's the fan/APS, as that's what the error code suggests. The fan and APS seemed fine. Regardless I bought a brand new APS yesterday and fitted in myself, as all I had to do was disconnect and reconnect the wires and the pipes. It worked like a charm, until this morning when I had the same issue all over again.

What baffles me is sometimes boiler works without any problems and sometimes boiler won't fire up and will start showing me this exact error code. This has been going on since last week. I don't know why would it work fine sometimes if there is a problem with the APS/fan.

Any help is greatly appreciated.
Thanks in advance

It’s classed as Gas work so no advice sorry.

You are playing with possibly the most dangerous safety device in your boiler, please leave it alone and call a registered gas engineer, it is against site rules to give you any advice on here about Gas work