Any ideas where to buy one with a gauge port? Can't find one anywhere. Last one I bought was about €15 in Bricomarché ten years ago complete with gauge.

https://www.bes.co.uk/safety-relief-valve-3-bar-with-gauge-1-2-bsp-f-x-f-11348/?ref=gs&rnd=19162&gad_source=1&gad_campaignid=21012711577&gbraid=0AAAAAD9gc2mVECgcbpg7CdX1NW1RhHhw8&gclid=CjwKCAjwtIfPBhAzEiwAv9RTJhKb9d79ZHl7dU95cWioRx5NQfKZiwdE5sIeMV3HLlrG93fe8cOZehoCZXIQAvD_BwE

 

Assuming your valve is 3 bar, there is a fuller selection on a  Google search if the thread configuration does not match yours.

Thanks! I looked at BES earlier and didn't find it. 😀