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Re: Grumman Solar Hot Water Heater

  • Thread starter Malcom \Mal\ Reynolds
  • Start date

Malcom \Mal\ Reynolds

Jan 1, 1970
phillb said:
The Grumman Sunstream CF100 Solar Hot Water heater I have is old, the
storage tank is rusting and the control box is on the frits to often..
I want to change to a storage tank that has a heat pump within it, but
no one makes this

I don't know about "within" it, but
here's some that have what I think you
are asking about


Apr 1, 2010
Apr 1, 2010
Grumman Energy Systems Controllers

I worked on dozens of the CF-100 modules. Your controller problems could just be a wire or a sensor issue. That IE C-30 controller in the CF-100 was made specifically to mount in the Grumman closed loop module, so you won't likely find any of those around (it has the special mounting plate on the back). I closed my solar servicing business about 6 years ago (in San Diego) and may have kept some GESI controls, etc., but they are pretty well hidden in boxes in my garage. I'd only go hunting if it was gonna be worth my while...

That being said, the sensor/wire connections at the roof are probably the biggest thing to fail since they're exposed to the elements (weather, rodents, etc) at the collectors. The 10k ohm sensors used at the collector and tank are standard 10k ohm thermistors. You could get replacements at Goldline or other solar sources. I'd suggest getting two new sensors, and hooking them directly to the controller; then, with cups of hot & cold water you can test the functionality of the control box. Hot @ collector sensor and cold @ storage sensor connections should turn the pumps on and vice versa.

I started to write a book to help you with other issues you'll probably face with the CF-100, but it didn't seem fair to post it in an electronics forum.

As for the tank, I've only had a limited experience with air-to-water heat exchange heaters, so you'll have to follow up on that yourself. I don't see any issue with hooking up a heat exchange tank to the solar system, as long as you still have 4 nipples available for the cold/hot and solar supply/return.

If you still have questions, contact me at jmkeene at tampabay dot rr dot com. I used to have copies of the Grumman CF-100 manual, but I probably tossed them awhile back when I purged all my records. I don't remember... Most of what you need to know about these modules is burned into my brain anyway. I only found this message because I did a web search for Grumman Solar Energy panels to see what some brand new 3' x 7' G.E.S.I.'s might be worth these days. I've got a couple of those sittin' in the garage, too.

Hope you find this information helpful.


Here's the IE / Goldline link
Independent Energy Controls are now Goldline Controls

GL-30 Solar Control
Differential temperature control 120/240 VAC input
8-20ºF adjustable turn-on differential 20A, 2HP output
4ºF fixed turn-off differential LCO includes line cord and outlet
110-230ºF adjustable high limit


Aug 3, 2010
Aug 3, 2010
Grumman Sunstream

I have an operating system, of course I've had to replace the tank and a controller in the past 30 years. If you'd like some ideas on how to keep this operating drop me a line at

I'd be glad to help you out