Hi ray. You don't say which rad you are going to change, if is an upstairs one or downstair, if it is upstairs you will only have to part drain the system, the way I do it is to turn off the other rads at both sides and then find the drain cock which will be at the lowest point but could be on one of the rads. connect a hose pipe to the drain cock and open it, then open the rad that you are going to remove to allow the water to drain when you have fitted the new rad open the other rads at both sides then open the filling loop on the boiler till the pressure is between 1 and 1.5 bar (check you user guide) then start bleeding the rads untill all the air is out of the system and bobs your uncle (you may have to top the water up in the boiler as you bleed the rads)
11, April 2005