Tom,
All you need is a cheap thermostat. Just put the contacts in series with the relay coil.
Yep, you're right, Frank. Why didn't I think of that?
The spare one I have here is a standard room thermostat and goes down to only 50 degrees, so will have to take a look on the web for something that works below 30F.
I think most are 24VAC too, so will have to find a 120VAC version to handle the timer circuit or add a second buffer relay.
I'm finding that 5 minutes every hour turn-on rate is too often. The pipes stay warm longer when down around 15F outside. So I will try 3 minutes every 1.5 hours for now.
T
