Should have probably updated this thread a few days ago but i'm still trying to figure out what's what!

My solenoid valve needed replacing but that was not the culprit. It was leaking when water was pumping through but this was not the cause.
I tried to use a small funnel and try to hear for any distinct hissing noise from any connections but i couldn't detect any leak this way.

I'm thinking if it's possible that the rapid decrease in pressure is due to having the cover panels off the machine. I guess that 2-3°C decrease in such short time might be normal for a non-insulated boiler, that is in direct contact with air that is around 100°C less than the boiler temperature.

I still haven't ruled out the possibility of a slight leak though, so i was planning to get my hands on some glycerol and see if i can detect a leak this way.
If i don't, next step is to put the panels back on and see what happens then.