October 23, 2014

Tech Tip: iSolar Controls

The intent of Ask Caleffi, was to make it as easy as possible for installers and contractors to understand and utilize our products. One of those products is our line of iSolar controllers. We understand that plumbers, solar installers, and hydronic experts are not all controls experts. With this in mind, over the past year here at Caleffi, we have expanded our video and digital offerings to make our products easy to use and understandable. Check out some of the videos we have put together, as we mash together Tech Tip and Throwback Thursday!

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Kenneth Christison
November 13, 2017


I received a service call on a Calleffi pump station with an iSolar Plus controller that as in error state. I found a blown can fuse. I replaced the fuse and it blew again immediately. I tried to turn the pump manually, with a large screwdriver, and was not able to move it. My supplier and I discussed the situation and decided to try a new Grunfos replacement for the Wilo original pump. I have replaced the pump and re-wired everything. The wires at the old pump showed obvious signs of heat damage so I cut them back a few inches to find good, normal looking conductor wire and insulation. After re-assembling everything I installed a new can fuse and plugged the pump connected the power cord to the receptacle. The controller shows no sign of power on the screen and the can fuse does not blow.Tthere is 120V power at the receptacle. Is the controller blown or is there a reset procedure?

I would greatly appreciate any help you can give me to resolve this problem!

Best regards,
Ken Christison

Cody Mack
November 27, 2017


Terribly sorry for the late reply! I know that we spoke over the phone not too long ago about this situation and it seemed that the control had failed. I hope your repairs went smooth.

If you have any further questions, please let us know!

Best Regards,

Cody Mack
Applications Engineer
Caleffi North America

Cory Fouquette
October 18, 2018

I have a customer with a solar thermal system for domestic water heating that he does not use because he has so much trouble with loosing glycol solution out of the Spirvent air eliminator. I have had issues myself with micro-bubbles in glycol mixtures that seem to make auto air vents leak out some glycol with the air. What would you recommend using? Its a 1-1/2" main on this system, so would be looking for a threaded model. cfouquette@corporatemechanical.com 612-328-3284

Scott Hughes
September 16, 2021

I have an iSolar 1 and the solar pump is only getting around 78 VAC across controller connector #17 and #18 when the solar pump is blinking on the display. Input power is 120VAC across controller connector #19 and #20.
The unit is old can it be fixed?
If it can not be fixed, which new controller should I buy?


In reply to by Scott Hughes

September 20, 2021

Scott, I would confirm you voltage coming into the control and then measure the voltage at relay 1 terminals 17 & 18 with the solar pump disconnected. If you measure 120v than the pump could be causing the voltage drop. If you still measure a voltage drop you may want to check the ground or neutral of the incoming power to make sure you have good connections. You can always call Caleffi tech support to discuss.