Ross Kirkland
There are multiple things that could cause this, assuming it's a combi boiler, it could be the cold inlet pressure is too low or too high. If the pressure is too high, then the boiler may not be able to heat the water quick enough to keep up with the pressure and therefore flow at taps, the boiler manual will state the correct range of inlet pressures, the easiest place to measure the cold pressure is to plug in a pressure gage where washing machine is connected, if the inlet pressure is too high, then a pressure adjusting valve on the cold inlet pipework would remedy, or re-adjustment if one is already fitted. I have also had it where an existing pressure adjusting valve was set to low, meaning that the boiler was not getting enough flow/pressure through it and this was causing the boiler to overheat. The flow sensor or diaphram within the boiler may be faulty, meaning that the microswitch is flicking on and off causing the boiler to cycle on and off. There could be a number of other faults within the boiler that could give similar symptoms. Whilst the water pressure issues can be investigated by diy or plumber, if it isn't either of these, then gas safe heating engineer is required. Job can be posted in job section to get quotes for plumber or heating engineer.
