Pressure keeps dropping?

Dear Sir

I would be grateful if you could help me resolve a problem with my Worcester Heatslave 20/25 - RSO-GB-L Oil Combi system. I am experiancing pressure loss problems with the pressure dropping from ~2Bar to zero bar in usually 2 days.

I have inspected the system, (although have not removed the silver insulation), but cannot find any leaks other than a very small leak coming from the 1/4 turn valve located at the top of the boiler. I know this wouldnt help with the pressure loss, but wouldnt have thought this to be the root cause.

Incidentaly, in the time it took me to take a few photo's of the system I noticed that the pressure reading on the front mounted pressure gauge suddenly jumped from 2 Bar to 3 bar; I am not sure if this is related or not but again wouldnt have thought the pressure should have varied so much, (please note that the system was turned on, and had been on for ~2hrs before i took the photos).

The details of the system are as follows, any feedback you can offer would be greatfully recieved;

Serial # 7716100084 2870250585
Model veersion AWA
output 25kw max/20kw Min
Boiler pressure 3 abr max
Controller Temp 55-82 centigrade
Nozzle 0.75 USG 80 degrees EH Dantoss at 105 PSI