You provide precious little information - heating systems are not all the same...
They sometimes have a valve to send the heated water to hot-water tank - radiators or both.
Yours may be stuck...
This video will explain it a bit...
https://www.youtube.com/watch?v=Yyn_fBEH90U
If you have a hot water tank with an immersion heater
then Bob's your Uncle!
You will be lucky to get hold of a plumber before the Christmas holiday.
Good luck...
Peccavi, December 2012
