Troubleshooting Tekmar 156 Differential Controller for Solar Electric Water Heater - any help appreciated

[Pajamarama_64]

Hello, I’m a residential service & repair plumbers apprentice in Southern California. Replaced an 80 gallon solar electric water heater for a client, replaced everything same for same as it was and used the recommended Tekmar 156 controller, to replace the old GL-30 controller.

Having some difficulties in programming the controller correctly to tell the heater when to kick on its heating element, or rather when to kick on the pump and cycle hot water down from solar collectors on roof. Currently, while we have a few cloudy days, the heating element in the 80 gallon tank is off, temp shows about 80 F, and the solar collector pump is also off, temp shows about 76 F on roof above. Posting some links to the controller below, any help at all is appreciated.

https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/42721-source/156-c-02

https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/42722-source/156-d-06

https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/42720-source/156-a-06

 

[JLV03]

I think you need to start with the basics.

What temp is desired in the tank? I assume this would be set by the water heater's thermostat.

Next, what is the temp difference (DELTA) to drive turning on the pump? 5F warmer at the panels vs. the tank? 10F? More?

Finally, looks like there is a max temp on the controller, what should that be? Desired tank temp + some amount?

There is also a min setting, but I'm not sure you need to play with that much for your climate.