This sounds like your central heating circulating pump has broken down and has to be replaced.
Metro, April 2010
seems to me that the circulating pump has packed up the reason that the upstairs rads are hot and the downstairs is cold is that the hot water is rising by convection instead of circulating by the pump
jagman, February 2010
edit
I can answer this question...
my radiators down stairs are'nt working but my upstairs one's are ?