No expansion tank on closed plumbing system

Just finished up my first mock inspection and I have a couple quick questions about a water heater without an expansion tank on what I believe to be a closed system. The home had a double check valve backflow preventer and reduced pressure backflow preventer in the front yard, side by side, that look like the ones pictured below. Every home in the neighborhood had these two assemblies side by side in the front yard. Firstly, why would there be two backflow preventers for one home? Secondly, I assume the plumbing system is closed: however, the hot water tank does not have an expansion tank. The top of the water heater is pictured below as well. Is this a glaring defect or am I overlooking something that allows the lack of an expansion tank?
Thanks in advance for any help and advice!
backflow preventer g
backflow preventer w

The RPZ is a single backflow preventer device, post pictures of what you actually saw. Most often if it’s outside, it’s used for irrigation/sprinkler system. If the water heater is piped upstream of the backflow preventer, the piping is not a closed system.


That’s an irrigation system manifold.


Depending on the municipality here in GA, if a backflow device is required for the domestic water supply the back flow device is found outside as often as inside. Maybe because of mild weather. But most only require it on the irrigation system or on commercial properties. I suspect the OP is in the way south because that is above ground.

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Hey Chris, how can you tell the difference between the two?

The two what? Judging by the four separate valves in my area that would be part of the sprinkler/irrigation system.

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I believe those are test cocks.



An RPZ on a residential dwelling? how often is this the case in Georgia? I highly doubt this to be the case.

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Regardless of this particular house, I find the expansion tank is missing probably 90% of the time where one should be there.

It’s even missing on my own house!


I agree, unusual. I only stated “most” because there might be an outlier. What some counties do have is a dual check-valve built into the meter.

I don’t report on the presence/absence of expansion tanks since we really can’t know how the system is setup. I suppose I could educate myself about the protocol in every water district that I inspect in but I guess I’m just lazy. The upside of calling these things out is minimal and the downside is you are wrong, slow down a transaction and make a bunch of people mad. In 22 years of inspecting and talking with lots of other inspectors I’ve never had or heard of a complaint regarding anything remotely closely related to an expansion tank. I’d personally spend my time brushing up on truly important issues and let this one go.

This is a perfect example of what I bark about daily… “Is it performing as intended?” That’s what we are there to determine. We are NOT there to question every code, manufacturer’s specification, installation and tradesman since the house was built.

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Heres a pic of the two assemblies. The set on the left is the home i inspected, set on the right is neighbor. The left assembly is the RPZ, right is the double check valve. There was an inactive sprinkler system on the lot

Until it doesn’t. I disagree with the premise it is not within the realm of a home inspection or is relegated to specialty tradesmen.

It is a simple inexpensive safety device that falls well within most home repair budgets.

This is how I navigate the lack of a missing thermal expansion device and educate my client simultaneously.

Water heater did not have a visible thermal expansion tank or device which is recommended for a “closed water system”. I was unable to conclusively determine if the water supply was an “open or closed” system and such determination is outside our standards of practice. Thermal expansion can create a rapid and dangerous pressure increase in the water. Recommend further evaluation and the installation of a thermal expansion tank or device as needed by a qualified plumbing contractor.


Yeah, this is a long and winding road that you could navigate with anything that is currently working the day of your inspection. “It’s working today but could fail.” It’s a design/installation issue that varies by municipality. Do you actually educate yourself as the protocol in each water district you inspect in? If so, you’ve go more energy than I do.

And, fwiw… your own comment says it’s “outside the standards of practice.” :slight_smile:

I HATE brining up issues that “might” be problems. Agents and buyers hate it to. They want to know what’s wrong. Obviously, we don’t always know but I really try to minimize the things I don’t know. This one is just pretty minor and I’d be surprised to ever see it turn into a liability issue for a HI. Of course, anything is possible…

No, and I do not need to. Regardless of municipality, I can make safety recommendation at anytime. Furthermore, it is often included in manufacturer installation manuals. Here is the verbiage from page 13 of the following manual.

As water is heated, it expands (thermal expansion). In
a closed system, the volume of water will grow. As the
volume of water grows, there will be a corresponding
increase in water pressure due to thermal expansion.
Thermal expansion can cause premature tank failure
(leakage). This type of failure is not covered under the
limited warranty. Thermal expansion can also cause
intermittent temperature-pressure relief valve operation:
water discharged from the valve due to excessive pressure
build up. The temperature-pressure relief valve is not
intended for the constant relief of thermal expansion. This
condition is not covered under the limited warranty.

A properly-sized thermal expansion tank should be
installed on all closed systems to control the effects of
thermal expansion. Contact a plumbing service agency or
your retail supplier regarding the installation of a thermal
expansion tank.


Another endless road… I’m sitting at my kitchen eating bar typing this and I can look at 20+ appliances, products and fixtures that “could” have safety problems. Should I make a buyer aware of every one and quote chapter and verse from instruction manuals of each? IMO, a big fat no. Not only do I want to see my family tonight rather than writing a 200 page report, it also opens me up to liability I’m not being paid to take on.

The guy that taught me this biz was a cranky old bastard that always talked about “managing buyer’s expectations.” He also had some theories about once you do something in one area you are responsible for the same standard of care in all areas. Examples being things like citing codes or manufacturer’s instructions. I’d argue that trying to make a home inspection too comprehensive/complete/precise opens one up to as much liability as looking past things we aren’t there to inspect for in the first place.

As always… great discussion. BTW… do you ever sleep? It’s 8PM in Hawaii and I’m about done. At least I know you’re not out closing down the nightclubs… unless you type REALLY fast on your phone? :slight_smile:


Yep, I have the same concerns. Opening up electrical panels, lifting ceiling tiles etc etc.

Finally, I do not passionately disagree with you about the tanks. But for me, it deserves and honorable mention for a few reasons. There is another inspector here who has concerns about condensate discharging to cast iron drain pipe. That does not even hit my radar screen. Certainly an “opinion piece”.


I am up writing a commercial report. House is quiet and I am in a zone. I just jump on here for breaks.


Better pic

There’s only one way to verify if those valves are upstream of the potable water. I’d make no comment about an expansion tank on the water heater without that knowledge.