My grandparents have recently had a new shower and immersion heater tank fitted. The system was working perfectly before, but know there seems to be air trapped in the system and they ain't getting hot water. its sort of warm. Although the pipe coming from the top of the immersion tank is hot, by the time it gets to the taps its only warm and keeps spitting out air. When you turn on the tap, water comes out at a good pressure then it coughs air and the pressure drops to a dribble then the pressure builds till it coughs and so on. No matter how long you keep the tap on the air never goes away. The plumber that made the changes has washed his hands of it and refuses to come back to sort the problem he has created. Any ideas of what is wrong and any suggestions on how to bleed the system??????? My grandparents are in their 80's and don't have hot water for the winter.