That's true, but what can we do about it unless we change the heating industry terms? The automatic coal stoker boilers often creep above boiling, but since they're under pressure, there's no actual boiling. Commercial boilers have a second aquastat with a maximum high limit of 240 degrees and manual reset, L4006E, so you want to avoid those near-boiling temps.

Boiler not furnace, yep check expansion tank and probably temperature sensor (aquastat I believe) cant rule out a bad valve even though its new, that or some gunk got in it making it stuck open (which is common)

One of my pet peeve's has been people who post on forums seeking assistance, asking for help, but then, once they find the answers necessary to solve their problem, don't bother reporting the solution leaving the string the dangling! It’s as though they don't realize that a public forum is not solely for their use or benefit but also (arguably more so) to serve others that will be searching for the same information about the same issue, possibly, for many years to come. I realize we’re all more motivated to write when pressured by those problems that need solving but, considering the time spent and efforts made by others kind enough to generously offer their assistance, taking a few minutes to post a solution once found is the least one can do. I didn't get back to this as soon as I would've liked to but I’ll not be one of those people so back to my story and its exciting conclusion. They've recently been replacing the main gas lines in our area. I didn't immediately see any connection but it seemed too much of a coincidence that these previously nonexistent leaks and drips should randomly begin to occur very near the same time that construction began. I talked to one of the guys which lead to talking to some of the other guys which eventually lead to speaking with the guy in the water department. What I learned is that the waterline in this area is, more or less, a loop supplied on both ends. In the event that, while excavating to install the gas lines, some sort of damage is done to the water line that necessitates an emergency shut off, they shut off the supply on one in advance so that, if needed, they could immediately stop it by shutting off the other side. This apparently caused an increase in the water pressure of the loop. He (the guy from the water department) opened up the other end and our pressure here dropped from 148 down to 120, apparently still considerably higher than normal or is desirable, but low enough to make a difference. All leaks have stopped. So, to answer my own original questions, higher than what is considered normal water pressure —but not necessarily in excess of its stated psi rating —will or can cause flow from a pressure relief valve. Also (I was previously unaware of this) other fittings, valves etc. throughout the house plumbing are only designed to withstand up to a certain pressure. As for me, I suppose I still need to install a pressure reducing valve but I don’t need to install one today. In the meantime, I may be able to pressure wash the house without a pressure washer!

I can't tell the size from the photo - but buy the 3/4 and a 1x3/4 bushing. You are covered both ways that way.