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Peterd123
The one nearest the top of the tank to the left in the pic. is rather loose and there is one above. Will have to get these checked I think.Just a idea. Has the installer fitted a new gatevalve feeding your cylinder and also left your old one in.
if your old one did not close properly he might of put one in after that allowing the water to be turned off.
Gatevalves can seize up, you can turn the head and it will keep turning, maybe it has seized when nearly closed.