If I had to guess , not knowing anything about solar, I would say that,,,, if the green wire is ground, which grounds the outer part of the tank, then is the black wire also grounging the tank? Or is it just missing a thermostat?
No thermister was installed on the bottom of the tank. Most solar DHW systems use a differential controller to operate the pump. The controller measures the difference between the collector temp and tank temp using two thermisters. When the plumber replaced the solar tank he didn't switch the thermister over to the new tank. He simply connected both wires from the differential controller to the lug where the thermister should have been bolted on.
There were other problems with the installation as well not shown. They piped plastic right onto the heater with no mixing valve. Solar systems can produce temps of over 250F in certain circumstances (like a malfunctioning thermister or diff. controller combined with low hot water consumption) and blow plastic piping apart. The heater needs to separated from the plastic with a tempering valve and heat traps ran in copper. Another issue is scalding. Can you imagine what would happen to a child that opens up the faucet or shower after coming home from vacation and 200deg water comes out?!
In short, he never should have attempted the job since he knew very little about what he was dealing with.
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