Closed loop pressure increasing

[Shifters]

Just wondering if anyone has even seen an issue with the pressure gradually increasing on a closed loop system where there is no fill loop attached. I'm seeing this issue on a gshp and whats more unusual is its on the cooling side. If it was on the heating side you could put it down to expansion but this water/glycol is gradually cooling but the pressure steadily increases over over a couple of hours from 1 bar to 3 bar before it eventually triggers the safety valve. I've never seen a system gradually increase like this. Has anyone ever had a similar experience?

 

[Deleted member 120897]

Sounds like something is bypassing, if there’s a hot water plate heat exchanger, consider this.

 

[ShaunCorbs]

Or coil eg unvented ?

 

[Shifters]

Hi, no theres no heat exchanger leaking its been pressure tested and nothing connected except a ufh circuit.
I'm completely baffled by it.

 

[Jonnyo]

Hmm is the Expansion valve failed in the heatpump

 

[Jonnyo]

Or is this where the ground pipe passes through the evaporator? Is the ground loop horizontal or is it a borehole.