On Sun, 30 Apr 2017 08:37:12 -0500, dpb wrote:

On 04/30/2017 6:29 AM, unk wrote:
On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:
...

To amplify, these boards retain their settings on power-off so if use
the NO contact and the "COOL" side so closes on TSetpoint, when power
comes back on the relay won't close to restore power to AC if the
temperature is below the turn-on setpoint.

...

It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above
freezing when the users leave. They are supposed to drain the water as
well.

But sometime they don't set it, and sometimes they don't drain the
water system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to the
pump) and a electrically operated valve, but for b) I need a switch
that will cut power to the relay.
...

You're still going to have to have aux power to operate the valve when
power goes out for a) then.


No, I'm getting the kind of valve that is open when there's no power.