I have a leak in an open CH system. It leaks something in the region of 1 litre / 10 mins when the system is turned off, when it's on, there does not appear to be a leak. Seems really strange to me. I checked the immersion tank which is a cross over point between CH and hot water system, I don't think it's leaking inside the tank, as the water is running in the CH tank while the hot water is not used.
I don't see any leaks in the house, so, I can only guess that it may be between the shed and house. I'm guessing that the heat is sealing the joint. Tried some sealer, which seemed to work but it's started again since....