I've been looking to replace my Ideal gas boiler. It has a C rating I think, it functions well enough, but I'd like to get an A rated one that's good and going to last a long time. So far,from speaking to a few plumbers/installers, I have been recommended to go with either a Worchester Bosch or a Viessmann. Apparently the Viessmann is the best, but naturally more expensive, and apparently parts aren't so easily available. I have been looking at the SEI site, and the UK CHeSS site ( gives info on various boilers). A lot of this stuff is complex, and I'm not sure I fully understand it. Any suggestions anyone? My house is an average sized 3 bed terraced.