this is just a guess.
Check the tap washer on hot tap.
Check the white whale pressure valve located under seat where the water inlet is. This is adjusted by turning the knob on top clockwise until its closed, activate 12volt system turn on the sink hot tap half way then adjust the pressure valve turning knob anti clockwise until the valve clicks and pump switches off. Cold tap should work ok, No different!
Then it could be airlock, or the none return valve on the heater cold inlet, for obvious reasons to stop back flow of hot into cold circuit it may not be opening fully so will need changing. Lastly check for leaks in pipe from heater we had problem with one push fit straight joint on shower/tap combo in toilet sink leaked so lost pressure at tap for hot water.
Good luck
Bob, August 2014
