I've scanned this thread and it seems that one important troubleshooting basic hasn't been mentioned. Apologies if I missed it. When a circuit like this isn't doing what you expect, the first thing to check is the "reference". In this case that is the input node of the op-amp (or comparator) that is connected to the POT. That shouldn't be moving with outside temperature changes, so if the regulating temperature is different at different times, compare the voltage at the pot-connected amp input at the two times. If that changes, then that's your problem. Then you need to figure WHY it's moving around with outside temperature. That's place to start. You need a decent 3 1/2 digit DVM to do this. These circuits are not that hard to trouble-shoot, start at the reference and work outward. Don't "shotgun" it. The reference is the point that telling the circuit what to do, in this case it's the pot voltage.