Only just recently had a Brit Gas bod here for two days, re-plumbing the airing cupboard, rodding out some pipes, replacing some plastic with copper, loads of upstairs floorboards up, fitted a filter and treated the system. It was he who recommended replacing the rads one by one as and when. This is the first one I’m changing. Yes it’s open vented but I’m wary of messing with the system too much now that he’s got all rads working again. I know I could tie up the ball valve in the loft, drain it all down and then add inhibitor before releasing the ball valve again but as I say, I’m wary of messing with it. I’m happy with the old valves at this stage. I could always change them all in one go at some time in the future.
Thanks for the suggestions though