My pervious house in Cheddar needed the boiler replacing, the Gas Board came and did the job. (Oh it was a combi system, no header tanks - I was going to convert the airing cupboard in the back room into a secret book nook!) anyhoo, after one year the boiler broke down, I had 2 separate Gas Board "Engineers" to look at it, (the second knew our very own Mr O'Doc as he lived in the same village) each diagnosed differernt faults and replaced parts - all to no avail, no hot water no heating! - I didn't mind as it was late spring early summer. I got fed up with this and threatened leagal action - sale of goods etc.... the Gas Board then sent a 3rd Engineer from the manufacturer to fix the problem, she walked in opened the boiler up, looked at the mess that the other "Engineers" had left behind, muttered a few unspeakable words, replaced a few things, and then took the control board out, explained to me that the work that had been carried out was to the most part "stabbing in the dark", because an updated controller had been released which fixed the fault I was having. A new board was popped in and tweaking a few PID'S in the controller and presto the system fired up and was running sweetly when the house sold a while back.
Nowt to do with the O/P's problem, but a boiler story that ended well