A long shot I know but I'm desperate.
We've had 5 separate plumbers/heating engineers come and look at our heating system which is continuously losing pressure. The last people stayed all day, said there was a problem with the valves and there definitely wasn't a leak anywhere. Changed the valves, the heating was much more efficient. Over the weekend the pressure dropped to nothing again. The heating engineers are saying there is nothing else they can do.
I don't suppose anyone has had anything like this??