I have a 4 panel SHW system which has been in operation for about 6 months now. The panels are flowing anti-freeze, and were used. The panel loop was pressure tested at 40# (about twice the operating pressure) for 2 days prior to filling with no signs on leaks, six months ago.

Recently on a cloudy day, I noticed condensation on the inside of the glass on two of the panels. There has not been any obvious pressure drop in the panel loop (at least so far), but I am concerned that there may be a pinhole type leak in these panels (or perhaps rain/snow melt getting inside the panels).

Perhaps the "right" thing to do would be to take the glass off and check for leaks, and see if the liquid inside is rain water leaking in, or anti-freeze. however I was hoping that there might be an easier way to see if this is needed. I suppose I could just wait a while to see if any obvious pressure drop happens in the panel loop.

Any other simple ways to figure out if that moisture in the panels is just rain water getting in, or anti-freeze leaking out?