Back up thermostat is a MUST!! learn from my mistake

[ctrlfreq]

If one tstat fails, IE dies completely, not just probe failure, then the flexwatt isn't going to get power anyway because it can't get through the dead tstat.

Right, and because the power is being cut off to it, it won't be able to alarm about the failure (no power = no buzzer).

Do Johnson Controls or Rancos shut themselves off in the case of probe failure?

It would also be interesting to know what constitutes a "probe failure" for each manufacturer (ie. a short or circuit break). In this case, the probe didn't fail, but wasn't measuring the heat in the correct location, so the thermostat was compensating for what it thought was a low temperature.