Our traditional oil fired wet radiator system has thermostatic valves on all the radiators except the four in an attached annexe (ex shop), although the annexe is a separate zone, so controllable up to a point.
I would really like to add stats to those remaining four rads, which means either getting a man in, or (gasp) DIY. Have watched various YouTube videos but all different. Some drain the whole system, some drain just the one rad being worked on, and some don't drain anything. It all looks very simple in theory, but in practice?
Plan A is to close both valves, open the bleed valve then partly undo the valve to be changed, allowing the contents of the rad to dribble into a bowl. When empty, freeze the pipe, change the valve, then (after allowing the pipe to thaw) open both valves and allow the system to refill itself from the header tank. Baring 'unforeseen circumstances', repeat for the next three rads.
A fantasy full of unforeseen gotchas?