Yes. We just had the hot water heater replaced and an expansion tank was installed. The tank that we replaced also had an expansion tank. I believe that the tank we replaced was the original.

Even if you have an expansion tank installed a pressure relief valve is necessary and required by code.

We have one. 2006 Duval. It’s a pressure relief valve for the incoming house water line. (Water coming into the house from the street). Ours was not capped when we bought the house new, still isn’t capped. If water comes out, there’s a screw to adjust inside the garage, inside the little door where the water shut off is.

I do not believe you are correct, our house a 2013 vintage, and ALL of the surrounding houses have expansion tanks and NO pressure Relief Valves, or drains like the OP posted.

I had Mike Scott replace my heater last year.
They said both are required.
Reasoning they stated is "what happens when the rubber bladder in the tank fails, which they do?"
The relief valve takes over.
The relief valve is also an over temperature failsafe.

(or maybe since all their replacement tanks have the T&P relief valves installed from the factory, they just leave it?)

Mystery solved .

The picture you posted shows the drain to the original pressure relief valve.

Since you have an expansion tank installed, it’s perfectly fine that the pipe is capped .

You can rest easy …. Leave it alone …..

The plumbing code is a detailed written document. You can't just say that something is "required by the code" without citing a section in the code that specifically requires it. But, several posters on this thread have claimed that things are required by the code, with no reference in the code to back it up.

I have no desire or interest in “backing it up”.

If it’s that important to you then research it yourself ! Then you can post that everyone else is wrong …. Don’t forget to post the refuting documentation ! LOL !

All I need to know is that if it was not required BY CODE then The Villages would not go through the extra expense in installing it ! They are all about “The Benjamin’s”

Proof enough for me ! LOL ;)

2020 FLORIDA BUILDING CODE, PLUMBING, 7TH EDITION | ICC DIGITAL CODES
504.4

"504.4Relief valve.

Storage water heaters operating above atmospheric pressure shall be provided with an approved, self-closing (levered) pressure relief valve and temperature relief valve or combination thereof. The relief valve shall conform to ANSI Z21.22. The relief valve shall not be used as a means of controlling thermal expansion."

Edit : I do think that covers it !

That is a valve that comes pre-installed on all water heaters. Not a valve installed inside the garage wall.

Don't think so ! 505.4 covers water heaters. The valve shown by the OP is not on a water heater. It is a pressure relief valve for the house system pressure. If it wasn't required by code, it wouldn't be there.

IMHO what we are seeing is that Codes keep changing and construction practices also change. I am including the picture of the top of a water heater included in a post above. It shows the current code 2020) required elements:
1. Inlet cold water with block valve and outlet hot water with NO valve
2. The expansion tank shown with red arrow.
3. The pressure/temperature relief valve in the center relieving to a PVC line discharging behind the water heater.

What is not shown, is the detail of the pressure/temperature relief valve flowing to the drip leg pipe with NO restrictions and an air gap.

In about 2006, plumbing codes added non return valves (check valves) at the meter to prevent backflow from the house into the water distribution system. In turn expansion tanks were now required.

All homes I have owned since at least 2000 have had the current code setup with expansion tanks and PRV's discharging to the floor or drip pan. I have never seen this hidden valve setup with adjustments at the water inlet. This arrangement apparently was a standard practice in TV circa 2006 or so as described above. IMHO and experience designing utility systems for Refineries, all pressure relieving devices must be accessible and discharge to a safe location which for potable water can be to grade.

My suggestion is for everyone to look at the top of their water heater to confirm that they have an expansion tank and a Pressure/Temperature relieving valve installed. If you have these, I see no reason for the in wall PRV to this drain. If you have a hidden PRV behind the sheetrock, check to see if you have leakage and talk to your plumber about removal.

The hidden valve may be a small capacity thermal relief valve designed to release small amounts of water that need to be removed to decrease the pressure buildup caused by water in a closed section of pipe/tank that gets heated. This is precisely what the expansion tank does. It may have been a cheaper way to handle water expansion due to heating before expansion tanks became a code requirement. None-the-less, it should not have been hidden inside the wall IMHO>

You should also be aware that expansion tanks only last 5 or 6 years. Check them by tapping on the expansion tank to confirm some air space see you tube for examples. Two have failed here in our neighborhood, one with water damage.

PVC pipe
 

I had a constant drip from this same PVC pipe (patio villa, same location though). I called Kylie Plumbing after weeks of constant fast drips. Said I needed an expansion tank for my hot water heater. Once that was in place ($260 later) the dripping stopped. Then, two years later, 2022, I replaced my hot water heater and (Curry Plumbing from Ocala) plumber also replaced the expansion tank. I still have no more dripping from that pipe. Hope this helps.