I have a Vaillant TurboMAX plus 837 combi boiler which is mis-behaving. The heating seems fine (although I may not have noticed any problems with it I guess) but the hot water is mostly distinctly coolish (although not actually cold). The actual temperature seems to vary every time I switch it on - sometimes it seems completely fine but this is getting much rarer. One confusing thing is that the temperature display on the boiler panel claims that the temp is getting up to around 55C as it should be.
Any ideas? Looking at the schematic on the Vaillant site, it looks like a sticking divertor valve could be the problem though I don't really understand the termperature display bit. Is this likely on this boiler? If so, is it any easy part to replace?
Many thanks Mark