Help !!! Our boiler drops in pressure over a period of 3-4 days it will drop from 1.5 bar to almost zero so we are regularly refilling the boiler. There is no water coming out of the outlet outside. also not sure if its connected to the boiler pressure dropping the temerature fluctuates but only in the shower (we have a mixer tap). we have tested running the water through the all taps and the temperature remains constant. (including when it is run through the bath mixer tap) when it is flicked to the shower approx 1-2mins the water will go cold and the temaperture gage on the boiler drops. after testing this a number of times on the shower, with the temperature dropping regularly. it suddenly remained constant for well over 5mins. and only when cold water was added did it begin to fluctuate again and the temparature on the boiler drop. we have had a service carried out, new thermistors fitted. but nothing seems to solve the problem, any suggestions welcomed before we go to a lot of expenses trying to trace a leak in the pipes.