Unvented system losing pressure

[alexb1234]

Apologies for the lack of terminology, I've no idea what I'm looking at.

I have an unvented system - The cylinder is a Santon Premier Plus.

We've recently had the bathrooms re-done, and the mains water was shut off, so this may be related.

It appears the system loses pressure.
The only 'symptom' I have of this is this little dial -

The plumber said to turn both of the little black taps to the left...
This results in the black needle 'rising'

I let it rise to where the red needle is.
But 2 days later, it's back down to where it is in the photo.

There's no obvious signs of a leak (no water through the ceiling or anything)

There's also no loss of pressure on taps.

The boiler also still works and fires up

Any idea what's up?

 

[Madrab]

Any idea what's up?

Yup, it's losing pressure.
Wouldn't be anything to do with the mains water, no. Follow that copper pipe that's going down and out somewhere and see if it's dripping out of that. If you're not sure then I'd suggest you get someone in that can at least confirm where the pressure is being lost.