Glow worm Swift Flow 80e losing pressure

[sugarbabyluv]

I've a swift flo 80e Combi Boiler which was recently serviced by BG. During the service they stated the expansion tank need re pressurising. The engineer drained the boiler - re pressurised the expansion tank and re filled the boiler and gave my boiler a clean bill of health. However, since they left (day after) my boiler has been losing pressure, albeit very slowly, resulting in me topping it up every couple of days due to the pressure falling to 0.5 bar. Apparently the pressure should be a minimum of 0.7bar. When I top it up I pressurise it to 1.0bar. I can and will get BG back in but why does this now happen? Thanks

 

[kevplumb]

is the prv pipe outside dripping

 

[sugarbabyluv]

No - I've had my finger in it (oo er) Bone Dry. I've also chacked all my rads and can't see any leaks

 

[pierrot]

I`v hads a swifty that was leaking from a union inside the combustion chamber, was a very small drip etc but which evaporated from the heat inside chamber.