We get a small leak from around our hot water cylinder when the power to it is switched off. I am not sure if the leak is coming from the cylinder or the pipes supplying hot water to the house. There isn't a leak when the cylinder is turned on.
I'm not sure what could be causing this but if it’s your cylinder it HAS to go. A leaking cylinder is anything but good. You might like to try getting in touch with an excellent cylinder manufacture in Scotland:
You need to trace exactly where the leak is coming from.
If its from the cylinder then it's a new cylinder I'm afraid. If so and your system isn't fully pumped then current regs say that must be upgraded as well when fitting a new cylinder.
If it's from the pipework then that's probably an easier situation to deal with - but you must trace it.
Some years ago I had a leak from the seam around the top of my hot water cylinder. Managed to stop it using Plastic Padding's Chemical Metal product. However the leak returned after about a year and I had to change the cylinder. What you say about the leak stopping when the system is switched on suggests that the leak may be on a joint in the pipework, maybe one of the cylinder connections. As others have said, you need to find out where the leak is.
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!