Home Automation - Hot water recirculating controls (schematics)

I want to install a hot water recirculating system. I want a momentary (on) switch to energize the circuit, then have a thermistor set for 105 degrees to de-energize the pumping circuit. I need help in designing that 12 volt energizing/de-energizing circuit. Thanks, DIYBC

You know they already make these, with the valving, pump and everything you need to install it, for under $200..

You can buy from Grundfos the under-sink thermostatic valve (about $37) that will allow recirculation via the cold water (or separate) line and then close when hot water arrives. Then all you circuit would need to be is a timer; quite a bit easier to design/build.

This is really a simple control circuit. You would not use a thermistor to stop the pump but a themostat. Or, what I would likely do is just a delay-on-release timing relay. Simply use a 24 volt "wallwart" power supply to a Potter & Brumfield type CNS-35-96 timing relay. Adjust the "time delay to off" a few seconds longer than it takes to get hot water to your faucet. Run low-voltage wiring to the pushbutton mounted near the faucet(s). Multiple pushbuttons may be run in parallel with the first.

http://relays.tycoelectronics.com/datasheets/CNS_DS.pdf

Thanks for your replies! Furd, where might I find said timing device? I live in the Chicago area. Or is there a convenient source via the internet? Thanks again.

Simply do a Google search for CNS-35-96. You will also need the 11-pin socket, a 24 volt (AC or DC) wallwart, an enclosure and the pushbutton switches and wire. Be sure to shop around as this particular timing relay cost varies from about $65. to $80.

If you check the link in the prior post you can see how such a circuit would work. With that information you can perhaps find a less-expensive timing relay. Be sure to use one that will operate on no more than 24 volts.