Hot water problem?

don't blame the poor bloke who has done the radiators. Check main cold water pressure, sounds like it could be high, this causes havoc with shower valves and boilers, they are only designed to cope with about 5 bar pressure max but that is still high, a pressure reducing valve PRV can be fitted to control the pressure usually factory set at 3 bar but better to reduce it further to about 2 if not detrimantal to other things in the house. Also could be your thermostat in the shower valve going funny

RAWPLUMB
December 2009