Our central heating/hot water is playing up. Whenever I turn the system on for hot water only, after about 5 mins I can hear loud banging noise coming out of the Hydro Spartan Recovery tank. But if I switch on heating and hot water then there is no noise. I have just got someone in to take out the Spartan vessel, give it a good clean then put it back in again but the problem still exists. Can someone please help.