Had a new bathroom fitted approx 4yrs ago now had issues with the Salamander pump from day one so swapped to Stuart Turner got a 2 bar Positive head pump but still had problems so got a plumber in who told us it had been installed incorrectly. Had a Surrey valve fitted to the hot water tank & a dedicated pipe from the hot water to the pump also had a new Stuart Turner 2 bar Universal pump installed however we started to get no hot water coming through if you turned the shower to cold it blasted through but turn it to hot only got it dribbling out eventually after turning from cold to hot numerous times the hot water would start coming through full force & the shower would work pretty much ok for the rest of the day. After googling & talking with the plumber plus having an issue in the past decided to change the thermostatic bar. When first done all worked ok but next day got same issue but if you switched to the hand held it starts running fine & can switch back to the overhead. Anyone got any ideas why it is doing this? Everything is now plumbed as it should be now