Steca 20 amp controller problem

I have used Stecca controllers before but am not sure what model you have. My only suggestion is to check that the negative side of the panels is not earthing to your caravan and in turn the battery. Whlilst most vehicles and appliances these days are negatively earthed, my Stecca controller was manufactured as positively earthed and malfunctioned when i effectively had a common negative earth between the battery and panel. Typically you would not notice until you had a really sunny day and the controller did a lot of shunting as the battery was fully charged.

I had to ensure there was no common circuit between the negative side of the panel and the negative side of the battery. I've since moved to another brand of regulator that is negatively earthed.