Why ask such a silly question, are they upstairs or downstairs rads, have they been bled and are they switched on?
Do they have TRV's? If so, they might need unsticking... Are they getting luke warm at the bottom and not at the top (Need bleeding) or are they luke warm at the top and cold at the bottom (Normally sludge)....
So many possibilities, you need to be more specific.
GasAid.co.uk, December 2006
