Help ma boab!
Had bother with my first combi in the last house that I bought.
It was a cheap first generation Ferroli combi fitted in about 1986. It was hell getting spares for as the company that brought them in went bust not long after. Had to get spares direct from Italy. Which just amounted to the odd temp control switch and pilot light caplilary. I did a couple of times get a so called 'gas engineer' out to look at it, but cos they could find no detail or record of my model they wouldn't touch it, so I fixed it a few times myself before deciding it was well done. I kept the darn thing going for the best part of ten years, it was absolutely focced by the end.
Then I got an Ariston (non condensor), which had the addition of electronic ignition and a fan flue. I was amazed how much things had come on, both in terms of pumping out the heat, reliability and hot water temp control. It broke down once, the fan for the fan flue was bust. Was resigned to ordering and fitting a new fan, but I had a fiddle with it and found a little grain of corrosion had got into it and jammed it. Bingo, freed it off, and away it went again. Other than it, it needed it's expansion tank re-pressurised once. 7 years near faultless use.
The house I'm in now has a Vokera combi (non condensor) fitted going by the details around 2003, it's run for the best part of 2 years with me now with no probs (touch wood) It probably gets an easy time right enougth as I've fitted a stove to this house, and there's just me to heat water for.
I think you've been unlucky oldmotherfoccer, I'd get shot of that one. When the Vokera gives up the ghost it'll be another combi for me.