we have a very old boiler and water tank and every now and then maybe once a month or so they make a very loud banging and clanging noises it seems to be coming from the boiler and the water tank at the same time its really loud and scares me to death it sound like the boilers going to blow up! the only way to stop it is to flick the switch that in the cupboard where the tank is? any advice would be much appreciated, thanks.