Occaisionally when the hot water is run for a period of time eg fill a sink or bath, a terrible water hammers starts and will only go away by turning on a cold water tap at various and or different locations around the house. There is no pattern and sometimes the answer is flushing a toilet sometimes upstairs or sometimes downstairs. It recently went away after a new diverter valve was installed but after a week or so returned as before. The valve had to be replaced BTW, it wasn't as a solution for this problem, it was an as well. Any ideas?
