Thanks for the reply Simon.
Being new to this plumbing malarky - do you mean the thermostatic valves on the radiators?
As the problem occurs when the central heating is off I would have thought i could elimate the radiators?
When it happens in the middle of the night it appears that it...
Recently had a new combi boiler installed but had problems with water hammer ever since. Pipes rattle around the house and it can be stopped if you muck around with the thermostat valves on 2 radiators above the boiler., In the main however I need to go to the boiler switch it off and switch...