On 5/22/2021 11:41 AM, micky wrote:
In alt.home.repair, on Sat, 22 May 2021 05:30:55 -0700 (PDT), trader_4
wrote:

On Friday, May 21, 2021 at 10:09:46 PM UTC-4, DerbyDad03 wrote:
On Friday, May 21, 2021 at 9:29:43 PM UTC-4, Ed Pawlowski wrote:
On 5/21/2021 7:54 PM, DerbyDad03 wrote:
On Thursday, May 20, 2021 at 11:48:22 PM UTC-4, wrote:
On Thu, 20 May 2021 18:10:27 -0700, Bob F wrote:

On 5/20/2021 4:51 PM, wrote:
About a month ago my water heater (4ish years old) T&P valve popped off and wouldn't re-seal, so I replaced it. No issues for about a month, now it's dripping. I can"burp it" but drips again in a little bit. I'm wondering if I need to turn the temp down, I'ts where ever the factory set it, seems pretty hot. Not overly hot but hot. Thoughts??


Is there an expansion tank associated with this heater? It could have
failed.
That is my guess, if there is even a tank installed.
Back in the olden days the water expanded back into the system but now
they have back flow preventers and the expanded water has nowhere to
go.

Well, it's not a "timing" thing, it's a "system" thing.

Not all houses, even in these modern times, have backflow preventers.

Yeah, but most new ones do, especially if you have irrigation. My gas
fired water heat has an expansion tank too. Thousands of house built
here have them. Unheard of years ago it is now code many places.
I get that.

I was only commenting on the use of the words €œBack in the olden days
the water expanded back into the system...€�

In millions and millions of houses the water *still* expands back into the
system. Like I said, its not a €œtiming€� thing. What happened in the olden
days still happens, in many, many cases, today. Only the OP can tell us
how his house is set up.

I do find it interesting that the OP is handy enough to replace the T&P valve
but he apparently hasnt ever stuck a thermometer under a faucet.

Just knowing basic physics goes a long way. Heat water, it expands. Why don't
all pressure relief valves open? Water has somewhere to go. Where does it go
in my house? If you have a well with a tank, the tank is where it goes. If you
have municipal water, it goes there, unless you have a backflow preventer.
Like you pointed out, my house doesn't, nor do most homes here. New ones,
IDK. If you have a BF preventer and no expansion tank or a water logged one,
pressure is exceeded and valve opens. Haven't heard from the OP again.
Maybe the WH blew?

I think we discussed this before, but I can't remember the answer.

I just don't see how water expansion can be a problem. Prof. Google
says "Water expands about four percent when heated from room temperature
to its boiling point." so if I have an 80 (?) gallon water heater, it
expands at most 3.2 gallons, but a lot less than that since I don't heat
the water anywhere near boiling.

Recommended temp 125 - room temp 70 is 55,
Boiling temp 212 - 70 is 142

55/142 is a a little over 1/3 so if it's proportional, that's 1.4
gallons of exapansion.

Either way, don't the pipes leading to my house or almost any house hold
more than that? So that even if it backs up, it won't get into anyone
else's water? What do 100 feet of water line hold? Professor Google
says "The capacity of a 100-foot length of 1-inch diameter hose is 4
gallons." Maybe none of the water line to a house is 1-inch?


That is a lot of expansion. Since it is maintained at that temperature
expansion is really minimal except when the heater is running, taking in
cold water and adding a gallon or so to the system. Where does it go?
It does not compress so has to be forced out someplace.

If the pressure regulator is bad, that can be the problem too. It can
prevent backing up and/or is is allowing the pressure of the system to
go above the valve setting on the heater.

If you don't know the pressure of the system is is not possible to do a
competent job of troubleshooting the problem and finding the cause.

As for backflow prevention, the main reason is for a drop in city
pressure of system failure. Then your water can flow back to the city
pipes If the city drops, your water heater or home boiler is under
pressure and will go back so will sprinkler heads on your lawn
potentially siphon back with the fertilizer and dog **** from the lawn.