I have an Ideal Mexico Super 440FF conventional boiler fitted running 10 radiators over three floors. The house has a energy effficiency rating of D. Two rooms out of nine do not get warm- the radiators remain cool unless the temperature is turned up to 20 plus and then it is too hot in the other rooms. I have tried turning some hot radiators off, and also bled the offending radiators but all to no affect. Should I buy a new radiator- they are 15+ years old?

That is nice but what is the problem??