I realized I was sort of hijacking the thermostat thread so I am moving my question here.

Some times, if the water in the water heater is cold when we start, the pop-off is leaking when we arrive. Anyone else (besides my friend Max) had this problem?

I think it is pressure rather than heat, but I was thinking of changing from a 195* to a 180* thermostat. If we open the faucet for a second with the pump off before we leave (when the water heater is cold) it does not seem to happen. It does not have to be a warm day... i.e. the engine stays at 195*.

I can't seem to get a definitive answer as to whether our ('74) water heater pop-off is temp and pressure or just pressure. (I think the latter.)

Anyway, two or three times, we arrive and the pop-off is leaking and I have to flip the little toggle thingy to get it to seal.

Perhaps my answer is to change that puppy out... but I just helped my friend Randy get the anode rod out of his '77 and there was not an impact wrench big enough. (PB, let it sit. Bigger impact, etc.) We finally took the heater out and used BIG pipe wrenches and cheaters (six plus feet of cheater) I had not used for years. It finally came out, screeching all the way. I hope the pop-off in mine is not like that. It looks sort of newish. I have had a new one lying back in there, next to the heater, since Amana.