On Fri, 21 May 2021 16:54:03 -0700 (PDT), 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.

There is the International Plumbing code (2015 cycle cited here)

607.3 Thermal expansion control. Where a storage water heater is
supplied with cold water that passes through a check valve, pressure
reducing valve or backflow preventer, a thermal expansion tank shall
be connected to the water heater cold water supply pipe at a point
that is downstream of all check valves, pressure reducing valves and
backflow preventers. Thermal expansion tanks shall be sized in
accordance with the tank manufacturers instructions and shall be
sized such that the pressure in the water distribution system shall
not exceed that required by Section 604.8.

SECTION 608 PROTECTION OF POTABLE WATER SUPPLY 608.1 General. A
potable water supply system shall be designed, installed and
maintained in such a manner so as to prevent contamination from
non-potable liquids, solids or gases being introduced into the potable
water supply through cross-connections or any other piping connections
to the system. Backflow preventers shall conform to the applicable
Standard referenced in Table 608.1. Backflow preventer applications
shall conform to Table 608.1, except as specifically stated in
Sections 608.2 through 608.16.27 and Sections 608.18 through 608.18.2.


***********
It goes on to describe all of the code compliant ways to prevent water
from flowing back into the water system.