Dropping pressure in expansion vessel

Air to water virgin

Hi all living in a new build for the past 3 years , Air to water heating with underfloor downstairs and rads upstairs.

Whenever there is a long shower or a bath used the water pressure in my expansion vessel drops from 1.5 bar down to almost 0 bar.

This only happens after a lot of hot water usage.

I don't think it's a leak as if the showers aren't used the pressure isn't affected.

This issue only started couple of weeks ago , the first thing we did was got the expansion vessel changed (which was full of water)

Any ideas what the problem could be ?

Wearb

Is your vessel a white one? If it lost its charge previously it might have done it again.

Air to water virgin

No it's the red 18ltr vessel that is loosing pressure I am topping it up manually myself when pressure drops

Air to water virgin

This vessel

Wearb

Could you post another pic with a broader view.

Domestic hot water should not affect this unless its the wrong type vessel fitted or a damaged cylinder coil.

Air to water virgin

Is this any help

Wearb

It's too much of a tangle to be able to follow every pipe. You'll need someone on site to see why your domestic hot water affects this tank.

According to fitting instructions, your circulating pump is fitted in the wrong orientation, but that has nothing to do with your problem.

Air to water virgin

Cheers for the reply , I'll try to get someone out 👍