Hot water ok but my radiators are cold [lukewarm in patches sometimes] i've bled the radiators. The pump is running [well humming when switched on] but getting very hot. I'm guessing there is a blockage somewhere, if there is is there something I can put in the tank to cure this totally or will I need to drain the water from the radiator system. If that is the case what is the best way of doing this and then refilling it.
Many thanks for any help