Recently my shower stopped heating up, was only getting warmish water from it, assumed the thermostat had gone and decided just to replace it so purchased a gainsborough 10.5 deluxe which was pretty much a like for like replacement and now if you turn it up full the water is piping hot however move it slightly away from top setting and water is just mildly warm - so its either too hot to handle or too cold to enjoy - any ideas on what the cause may be?