Check to see if there is a room stat and if its calling for heat , if not turn it up. Otherwise check circulating pump is turning sometimes they stick and need a helping hand to move again by opening front and rotating shaft with small screwdriver.
plumber, November 2009
check for motorised valve see if it openes on request
anto brandon, November 2009
edit
I can answer this question...
the radiators not hiting but hot water it is what can i do?