Can anyone help have just changed bathroom suite sink w.c and bath, changed bath taps from singles to mixer head ! Before fitting turned water off at main and drained emersion tank down. After fit put water back on, tank that feeds emersion all OK ,think emersion OK but have lost pressure to hot taps on both sink and bath mixer , cold taps on both spot on confused!! At mo takes about 45 minutes to get enough hot for bath and missus not too h

Sure sounds like you've disturbed some minerals built up on the pipe walls that got sucked up in the system and is now cvlogging the inlet ports on your faucets. The solution woulkd be to turn the water off to the faucets and open them up. Check and clean the inlet ports on the cartridges.
Before you reassemble turn on the hot water to flush out the supplies and open valve bodys. Reassemble and test. Good luck. Tom