How to Tell If My Solar Hot Water System Is Working Correctly

This is some simple troubleshooting that the system owner can do.

Of course, things can become more complex and that is when you call in the experts, but don't be intimidated by your system.
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There is a very simple way to see if things are working properly:

Observe the system pump, on a sunny day, when you know you have water in the tank that is not fully up to 120F.

The system should “cycle” on and off, maybe 2 to 10 minutes per cycle.   If it is cycling then the sensor, controller, pump, panels, valves are all working correctly.

You can hear the pump slightly when its running, or you can put your hand on it and feel the vibration, but watch out, it can be extremely hot.   If you have the STECA controller, with the digital display you can also see the pump movement indicated, however, this does not prove that the pump itself is working.

If the pump is "cycling" then all is good.

If the pump  is not cycling or cycling on really long intervals, or really short intervals, then there is something wrong.

A common problem can be what we call a “vapor lock” in which an air bubble that was stuck in the tank or delivered via city water goes up to panels and blocks the movement of water, the pump cannot overcome the stuck bubble.   

This would pretty much make your solar work not at all.    And there is a simple fix for this….it is exactly what every owner should be doing at least once a year, and some recommend twice a year….the fix is called "the annual tank and panel flush"  

This not only is a required maintenance that is easy enough to do, it will also remove the air from the panels.    You will likely hear air spurting out of the hose when you  do this (I mean if there was air in the panels).     If you hear that air spurting out, then you can feel pretty good, that you have really solved the problem.

http://oahusolar.blogspot.com/p/hot-water-maintenance.html