So you bleed the system without the pump running??

As I said, we set the pressure to 1.5 bar, then saw it rise to almost 2 bar with the pump runnig. I then turned the boiler off and overnight it dropped back to around 1.5 bar (just under). There is no sign of water anyway. Most of the joins are soldered, it is only the caps that are compression fittings. What is the best thing to put on the joint to see if there is an air leak?? Washing up liquid?

Thanks again guys!!