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AMTROL ST-5 Thermal Expansion Tank
From the Manufacturer
Amtrol invented the thermal expansion tank to control pressure build-up in closed, hot water systems. This prevents the water heater pressure relief valve from opening, saves energy and eliminates a potential safety hazard. All Therm-X-Trol expansion tank
Stephen P. Hill
Reviewed in the United States on February 20, 2025
My old failed tank was the same model - this new one was dead easy to swap in. Following the instructions I lowered the pressure a little to match line pressure, put tape on the threads, pushed in the plastic "turbulator" thing, and screwed it on. Very easy repair saving a lot compared to calling a plumber - and I hate plumbing and usually pay someone else to do it.
Tracy Means
Reviewed in the United States on February 2, 2025
Great
Moog
Reviewed in the United States on January 7, 2025
Seems like a quality piece at a fair price. It does the job and is small enough where it worked out beautifully with not interfering with my gas Hot water heater vent piping!
Coachjpc
Reviewed in the United States on January 31, 2025
Worked great and easy to charge and install.
Mk5
Reviewed in the United States on May 24, 2024
This expansion tank is of excellent quality. installation was quick and easy. Saved me a ton of money by doing it myself as opposed to the plumber doing it. Took less than 15 minutes from start to finish.
anikko
Reviewed in the United States on February 21, 2023
This unit is a direct replacement from the one I had on my water heater. It was a perfect fit, unscrew the original and put on the provided Teflon tape and screw it on. Simple and easy.Update Sep/2024 - Tank failed in about a year. Seller did not respond to warranty inquiry. Not sure if they are even the real deal.The second tank blew after 6 months and give run around on warranty. Don't trust this brand, useless warranty! Don't believe just try claiming the warranty and you will get the run around.These tanks are garbage. The leak senor does not work. My tank diaphragm rupture for months and the indicator shows nothing. All gimmick. In addition, the tank is not stainless steel it will rust like crazy. Check out the photos.The third tank blew even before I installed it. Pressure the tank to 80 PSI source PSI and it just pop! Was rated for 150 right?
Silvertabby
Reviewed in the United States on March 30, 2022
I like the sight glass on the bottom air-fill Schrader valve that shows any water from a failed synthetic rubber air pressure bladder/diaphragm, necessitating tank replacement. I wish it also had a pressure gauge for accurate initial pressurization and ongoing monitoring to indicate any pressure drop over time, so I could add air as required. The air volume in the lower half of the tank is so small, that any momentary leakage while disconnecting a tire pump or pressure gauge from valve stem after charging, drops the internal pressure. I finally used a small compressor with a pressure regulator set to 80 psi and a hold-on air chuck to pressurize the bottom half of the tank to equal my static water pressure before turning the water back on to fill and pressurize the top half of the tank.It took a lot of force to push the plastic “Turbulator” down to seat it into the connector opening against the top of the pre-charged rubber diaphragm. I heard a brief “psst” that scared me that I had just punctured the diaphragm, but hopefully it was just an air bubble trapped between the diaphragm and the side of the top half of the tank. Again, a pressure monitoring gauge would tell if it’s maintaining pressure or not. My kitchen faucet and tub spout still drip intermittently, so adding the thermal expansion tank didn’t solve that problem. I designed and fabricated my own custom wall mount cradle out of scrap materials I had left over from other projects.
G. Lowitz
Reviewed in the United States on June 23, 2016
I purchased the AMTROL ST-5 to replace an aging WATTS version of similar size. While WATTS is a certainly a reputable brand, I was impressed with several AMTROL differentiators, including: 5-year warranty, made in USA (vs. Taiwan for WATTS), included water turbulator to reduce sediment in the tank, silver-ion infused polypropylene tank liner to kill bacteria, heavy-duty rubber diaphragm, and pre-charging to 50 PSI, making it easier to let air out during installation to match typical 40-45 PSI supply pressure. I also contacted their customer service department prior to purchase in order to clarify a few questions. I received a courteous and prompt response answering all my questions. Time will tell how well this unit holds up, but based on the thought and attention to detail in the design, I would expect years of trouble-free performance. This is a good value and would recommend it to anyone installing a new expansion tank. Also, check the AMTROL website for their sizing calculator to make sure your expansion tank is large enough. The ST-5 was suitable for our 50-gallon gas water heater based on the parameters we input, which includes the typical expected input vs output temperature differential, water pressure, and release valve limit. If you're not sure, contact AMTROL for technical support before you place your order.
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