bar valve

Hi all, So completely refitting my brothers bathroom. Got a 800 x 1000 shower enclosure. Concealed 2-way mixture valve which I’ve fitted. As you can see the inlets are 22mm. I suppose I need to just use reducers to 15mm? For arguments sake the top left outlet will go up and above the new...

My shower valve seems to be stuck on cold (my new flat mate seems to enjoy cold showers, so the thermo dial is being used for the first time in a decade). I was thinking of getting a plumber in.. but at £100 to £160 I am thinking that I could replace it myself. Is there anything I should be...