I have a hot water leak to my laundry wash basin and I am not sure what is the correct way to shut off the hot water so I dont drain the cylinder. I was told I can shut down all three taps (as shown in these pictures) but the big red one has a locking mechanism. The small red one is very hard to turn, but I have not put any force on it. The other black tap I can close (turning it clockwise) but then water starts dripping from it.
Any advice from plumbing experts out there?

