My elektra is a two-group machine. I noticed recently that whenever I operate the RIGHT group, water starts dripping from the solenoid and the grouphead of the LEFT group. The RIGHT group does not maintain its idle temperature normally either. At first, I thought the problem was vapor lock in the RIGHT group. Purging the RIGHT group HX solved the temperature problem momentarily but the dripping behaviour remains. Any thoughts? I guess it is one of the solenoid, but which one?

Thanks

Since the pump pressurizes the entire hydraulic system, the grouphead solenoids are the only barrier to water existing the group. So if the group A drips, it's group A's solenoid, independent of why the pump is running.

Similarly your temperature idle problem could be the same root cause due to "thermosyphon stall". That's when water escapes by a slow drip after the pump has stopped, slowly introducing a steam bubble in the thermosyphon loop. That prevents the water from circulating between the boiler and group when idle, resulting in a cold grouphead until some water is reintroduced into the line.

Randy presents a thorough explanation in Understanding and Preventing Thermosyphon Stall. The solution, in your case, is either cleaning dirty/scale from the solenoids so they close properly, or replacing them if the coils/plungers aren't closing completely.