Central heating has a circulator (pump) to circulate the warm water round yer arse.
Circulator has 3 settings.
Too fast and it'll make noises.
You've got 2 valves on each rad, one at each end.
One is the TRV, opens and closes on demand.
Other is lock-shield valve, should be set by plumber to ensure equal flow through all rads.
Water is a lazy cunt and will find easiest route through system.
( blaireau69 , the Cumbrian Travis Bickle., Thu 10 Nov 2011, 22:23, Reply)