We have just had a new water tank installed and have noticed since then that the radiators are now heating up when the water comes on! The heating system is switched off at the moment as it's the summer months (August!).

Has the engineer done something wrong and as a result are we likely to be using more gas/electricity? Should I make British Gas aware and get them out to rectify the problem?

Many thanks in advance.

This is out of my field but it sure sounds like you have a cross connection. Recheck your piping. Good luck Tom