I only have my water on (my heating is off) yet yesterday when I put my heating on for a few hours,I noticed that when I turned it off the radiator in my bathroom (which I can not regulate the tempertaure of as it isnt fitted with a temp control) was still on.
When I turn the hot water off it does go off but when I put my hot water on it comes back on.No other radiatirs are on.

belinda, August 2010

either the heating zone valve is passing or it's a bypass for your gravity hot water circuit. hard to tell without seeing the system layout.

Ian, August 2010