put it this way, a 64 layered aluminium foil disk over a 2" area has a burst pressure of around 1000psi.
Just to make sure no one is confused, a 1.5" union has an opening almost 2" across. I measured a 32 layer disk in a 1.5" union to burst at a differential pressure of about 400 psi, sometimes a bit more, so Spudfarm is probably very close to the mark in this case.
I'd be wary about this temperature sensing valve of yours. Unless it's insanely fast and accurate multi-thousand dollar equipment, most of the power will have been wasted to heat loss before it opens.