Recently had a new bathroom fitted and a new kitchen. The main stop cock in the kitchen has been moved and some new piping installed for radiators and fridge. The problem is that everytime we use and switch off the cold water (including flushing the toilet) the combi boiler fan is coming on and sometimes the hot water heating light comes on briefly. Its almost as if the boiler thinks there is a draw on the hot water supply. The boiler is only 18 months old and was working perfectly until this work was done. The bathroom and kitchen installers just seem to be scratching their heads and don't seem to know why this could be happening. I'm no plumber but I do know that the boiler should not be wanting to switch itself on everytime I flush the toilet or fill the kettle up from the cold water tap!
Any help or advice would be much appreciated.