agree with what bear said except i only have misgivings not hatred for combis
and if thats the system you have its probably going to be major expense/ upheaval to change to a conventional one so you're kind of stuck with repairing it or replacing with another combi – on the positive side no reason why a properly installed reliable make (vaillant or worcester bosch -yawn) shouldn't last 15 years
mr woppit – while i'm way too young for the IOW
the anti nazi league victoria park is a blast from the past for me too
went down on the coach from grassroots books in manchester with a motley collection of ageing hippies and radical punks – good times 😀
its usually easier than turning the mains off unless you need to work on the colds as well?
once its tied up it will drain the cold tank – roughly 25 gall
in theory you did right turning off feed to cylinder – unfortunately those gate type valves rarely shut off properly so tie up the tank and leave the gatevalve open
either do what stoner said and turn the mains off or just tie up the ballvalve in the big tank (bungee strap works well) the open hot taps till theyre drained