A quick pre-amble.... For quite a few months, we have been having problems with our DHW temp from our Worcester Bosch combi. Our regular corgi guy couldn't work out what was wrong and said we should call out Worcester Bosch.
Guy from Worcester Bosch turns up and says there is nothing wrong with the boiler and that the problem is with our Grohe 3000 thermostatic shower. He says that there is a problem with the NRV and that cold mains water is getting into the hot water side, reducing the overall temp. He says he has managed to demonstrate this by tapping the shower mixer and getting the NRV to close. He also says that this is quite common. I'm thinking that my regular heating guy should have known this and I'm currently £310 out of pocket with nothing fixed.
I pull both the NRV's from the mixer and sure enough, the one on the hot side is broken. I order a new set of NRV's and swap them over. DHW is now fantastic. The hottest its been for years. But the shower isn't happy now. All I did was fit new NRVs, I didn't alter anything else but now its running quite cool.
The new NRVs were modified parts and I thought that they may not be compatible so I tried the original ones back in there but no change. I have put the new NRV's back now. The only way I can get the temp up is to reduce the flow on the cold mains line in. You can get some sort of temp control via the knob but its not like before and if you want a cold shower (not that I do generally) there is very little pressure because of what I've done to restrict the flow.
Is the thermostatic cartridge knackered? It seems a bit of a coincidence or did the Worcester Bosch engineer damage something when he was hitting it? A new cartridge costs £97 but I've wasted so much money so far acting on the advice of professionals..... I want to make sure it definitely needs replacing.
Thanks in advance.