I have a Baxi 105e combi boiler and have a problem with the hot water tap on the bathroom sink. When i run the tap the pressure is fine until the water becomes hot then the pressure drops and starts spluttering - accompanied by a banging sound. Once i turn the the tap to full the spluttering / banging goes way. This is the only hot water tap which is affected the bath and kitchen sink taps work perfectly. Is there anything i can do to fix this? Many Thanks