Which knob…

[Welderpaul]

Do I use to turn off the domestic hot water?

 

[Morrisman]

Someone got a bit carried away with insulation there.

 

[pedrobedro]

Which knob Do I use to turn off the domestic hot water?

The one that installed it ?

 

[Agroshield]

Try the red one at the top of the tank. You would normally draw off the hot from the top (as hot rises). The black ones on the flexi near the red tank are the filling loop, so can be eliminated. The red one on the side of the tank is likely the heating coil.

Look up the connection diagram for the tank that is there (cannot read the name in the photo).

The blue stoptap in the street is a last resort...

Edit: there is not much harm you can do by trying each in turn, but clearly do not turn on something that is already off (like the filling loop).

 

[voipio]

Try the red one at the top of the tank. You would normally draw off the hot from the top (as hot rises). The black ones on the flexi near the red tank are the filling loop, so can be eliminated. The red one on the side of the tank is likely the heating coil.

Look up the connection diagram for the tank that is there (cannot read the name in the photo).

The blue stoptap in the street is a last resort...

Edit: there is not much harm you can do by trying each in turn, but clearly do not turn on something that is already off (like the filling loop).

What Agroshield said, though the red knob at the top of the tank looks like a gate valve, so may not cut off the water flow entirely. Some labels on the insulated pipework would have been useful.

There should be a stopcock on the cold water inlet to the tank, which should (normally) give a better stopping of the flow into the tank, and therefore the hot water, unless the washer in the tap has perished. How old is the system?

Is there only one expansion tank in the airing cupboard? If so, then the cylinder probably relies on an air gap in the top of the tank for the compressible expansion volume, which relies on the gap being re-formed from time to time.

There seem to be at least two pairs of flow and return pipes to the cylinder. Is this system connected to a solar thermal panel on the roof, or is there a hot water circulation system fitted, so each hot tap has near instant hot water?

 

[Barking Mat]

Try the red one at the top of the tank.

That's an over pressure valve isn't it ?

 

[voipio]

The overpressure valve is on the side of the tank, near the top. I (and I think Agroshield, too) was referring to the knob on the vertical insulated pipe coming out of the top of the tank.

 

[Seadog]

It's a wheel.

 

[voipio]

In the original image, the hot water cylinder looks like it's possibly a Grant Monowave. Which model/version is it?

 

[MattF]

When I first saw the thread title, I automatically thought one of us was in trouble for something.

 

[Blobber]

When I first saw the thread title, I automatically thought one of us was in trouble for something.

Did you have any one in particular in mind?

 

[brightspark]

When I first saw the thread title, I automatically thought one of us was in trouble for something.

guilty conscience

 

[MattF]

I'm simply that used to someone starting their sentence with those words. Automatic assumption.

 

[Erie Fred]

Someone got a bit carried away with insulation there.

"Lagging" and it looks like a professional/industrial job they made of it.
maybe paid by the hour or the amount applied ?