Long time ago, my heating stopped working, so I called out the expert. He quoted £250 to replace the extractor fan (Boiler wont work at all, if it cant extract gasses). I said I`ll think about it. I went out and bought a new fan for £150 from that place down Argyle Steet Industrial Estate. I fitted it easily and the heating then worked. I checked out the old fan, gave it a good clean and Wd40`d the workings and then oiled it and it worked like a dream... wasted £150. Ummmm.
Then it was my mission to never waste money again. Over time I have replaced the circuit board, the main valve, a red solonoid for the pilot light, a black solenoid for the main jet, the wire and ignition thingy for the spark. Learned to clean out the jet for the pilot light. Replaced the air pressure switch, which does something LOL . Replaced the plastic tubes which had cracked/perished to the pressure switch, I think that maybe it for now. Non of which cost me a fortune.
So, reading the manual could lead to fixing the boiler yourself if it does not entail gas connections.
Even so, you could look clever by telling the gas man what is wrong and not giving him the chance to over-charge maybe.
My boiler and I go together like cheese on toast :-)
One Way Or Another