Brittony water heaters are very reliable, main problems are diaphragm ,which you can still get,and pilot injector which can be cleaned, never buy a cheap combi , they are cheap for a reason
Get him to write out a little A5 poster on his printer, explaining what point he’s got to, then take them to the local plumbing merchants and ask if you can put it up , screw fix and tool station as well, good luck.