Some radiators warm most are cold

Until testerday the lower floor was warm but the heat was minimal on the upper floors. Now there is almost no heat on any of the radiators. What do I do? Does this sound like an expensive? I know nothing about heating systems. We've been in this house three years but I have not done any maintenance. Any advice is appreciated

have you "bled" the radiators? each radiator has a recessed "tap" you need a special radio ator key (about £1.50 from any diy store)you then "bleed" each radiator until water comes out.

Basically they sound like the radiators are full of air, which you let out by "bleeding"

TRY TO ADJUST THE LOCK SHIELD VALVES TO BALANCE UP THE SYSTEM IF SOME ASR HOT AND SOME COLD THIS IS LIKELY TO BE YOUR PROBLEM