Higher temperature water heater overflow valve?

http://www.youtube.com/watch?v=9bU-I2ZiML0

[video=youtube;9bU-I2ZiML0]http://www.youtube.com/watch?v=9bU-I2ZiML0[/video]

This entire thing is getting out of hand and it is too laborious to try to sort through all the "solutions". IF you do not have a pressure regulating valve, OR a check valve in the system then you have an "open" system so you do NOT need an expansion tank because the pressure buildup is absorbed by the city system. However, in that case the pressure should ALWAYS be the same as the city pressure in the street so it should NOT increase, or change, unless the city pressure changes and that seldom occurs to any great extent, assuming the main lines are adequately sized. If your pressure fluctuates, or slowly rises without using hot water, then you need a plumber to check out your system because that is an indication of a failing pressure regulator.

Ja, there are a whole lot of ifs with solutions based on conjecture. The first bit of conjecture was that the temperature stacking was the cause of the TPR relieving. I don't think there was any anecdotal evidence presented to indicate how hot the water got due to stacking. The boiling point of water at that altitude is nothing more than a distraction since the water in the tank is not at atmospheric pressure and so not affected by altitude.

The second bit of conjecture was that high city pressure was the cause. That I highly doubt.

There is/was also misunderstanding of how a PRV (pressure regulating valve) works in so far that it doesn't "regulate" the expansion pressure on a closed system. There was also conjecture that the absence of a PRV meant it was an open system and not subject to expansion caused pressure. There can be a back-flow preventer without a PRV present causing a system to be closed.

As in many cases, a prognosis is only as good as the evidence provided by the OP preferably without preconceived notions.

Just leave the faucet dripping and be done with it.

As a side note to this thread. I purchased two watts pressure gauges from the Home depot. Hooked first one up and it immediately rose to 100psi. OK...pressures a bit too high. Checked on it the next day and it still read 100psi. Deadman hadn't moved a bit. Removed gauge and yep...needle stuck at 100psi. Go get new gauge and hook it up...whoa...now I've got 180psi. Return gauge & head to supply house for "quality" gauge...damn...they are closed early for the holiday weekend. Hopefully they will have something better than the HD offering. Any suggestions?

Epilogue on all this: We had a pressure regulator put in, on the main water line coming into the house, just on this side of the big shutoff valve for the whole house, in the crawl space.

Before that, I installed a mechanical clock timer on the humidifier, so that it can only run for 30 minutes out of every 2 hours. That way it doesn't run for hours at a time and over do the humidity and cause stacking.

Between these two steps, so far so good.

The house pressure is now around 70 PSI instead of 80-100 and the toilets take a little longer to refill.

Thanks guys!