On my CH system I have 22mm (I think) pipe going to microbore manifolds. Off the manifolds there are 7 feeds each going to the 7 rads in the house. Each rad has a normal twist valve at either end but there are not TRV's. If I shut off all the feed valves on all the radiators (and the returns come to think of it) what would happen? The way I see it is that the pumped water can't actually go anywhere?