Hi timce If your hot water cylinder has been around for a while the most likely cause it that the heating coil has perforated. Presumably your CH expansion tank is higher than your cold water tank so you can check for perforation by tying up the ball valve in the expansion tank, turning off CH and HW and see what happens to the water levels. Regards S
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!