Amtrol ST-5 (Therm-X-Trol) is a water heater expansion tank, designed for use in domestic hot water heating systems to eliminate the potential hazards of water expansion. Water heater expansion tank is commonly installed in a domestic hot water system that contains a backflow preventer, a check valve or a pressure reducing valve. The patented InSight Indicator Cap changes its color when the tank needs to be replaced.
Applications: Residential water heaters, laundromats, dormitories, office/apartment buildings, restaurants, etc.
Features: - Eliminates the waste of energy and water, thus saving money;
- Protects the water heater and plumbing fixtures from premature failure;
- Reduces potential safety hazards associated with thermal expansion;
- Prevents a dangerous pressure build-up in the system;
- Prevents the relief valve from going off;
- Therm-X-Trol brand is the #1 choice of Professional Installers;
- NSF/ANSI 61®, IAPMO, SBCCI & City of Los Angeles listings.
- Factory pre-charged 40 psig
- System connection: 3/4" male threaded
- Stainless steel system connection
- Max. operating temperature: 200F
- Max. operating pressure: 150 psi
- Expansion tank volume: 2.0 gallons
- Max. acceptance factor: 0.45
- Height: 12-5/8"
- Diameter: 8"
- Shipping weight: 5 lbs.
5-year manufacturer's warranty.
Verified
Purchase
Nice quality tank. I've used these in many installs and they always do the trick. The stainless steel connections eliminate any risk for rust.
By Bob the builder (from Eastern Canada) on
11/25/2011
Verified
Purchase
boiler upgrades Both expansion takes went at same time time, replaced the hot water heater one with this, easy install, came with higher precharge 50 LBS which works better with my line pressure.
By Juan (from Bayville, NY) on
03/12/2022
Verified
Purchase
Exact fit works great
By Tony (from High bridge, NJ) on
11/02/2021
Verified
Purchase
OK Installed ,
By Artur (from White plains, NY) on
06/11/2020
Verified
Purchase
therm -x-trol Great tanks like all the features like a stainless male thread
By William (from Naples, FL) on
01/26/2019
Ask a Question
I purchased my home as new construction years ago and this model was installed. I recently purchased this unit again as a replacement but found the pressure in my house is 65psi. Is it okay to increase the pressure in the tank to match the home water pressure?
Yes, you can (and in fact have to) increase the pressure in the expansion tank to match the system pressure. You'll find the details in the installation manual.
By PexUniverse Customer Service on 02/04/2013
I am having a problem I am unable to check the pressure of the expansion tank. I replaced the valve stem and still nothing. The pop off valve is still tripping near the end of the heating cycle. When I put air into the unit my gauge on the compressor shows 40lbs. I am unable to check it with a tire gauge. Do I need a new expansion tank?
A common condition indicating that there's something wrong with the expansion tank is when the pressure relief valve goes off. If you're unable to check internal pressure, the optimal solution is to replace the tank. If you did not experience similar issues in the past, the same expansion tank model would be suitable. If you had similar issues when the tank was new, it may be best to get a larger model (1 size up).
By PexUniverse Customer Service on 12/12/2012
Sooo....you are not supposed to mount the tank horizontally. In a vertical mounting position, can you mount it with the InSight Indicator either pointed up or down?
Yes, either pointing up or down (the latter is preferred). For a vertical installation with the tank pointing up, we recommend 598-0210 (works for ST-5) for extra support.
By PexUniverse Customer Service on 11/19/2024
Can anST5 be mounted horizontally?
No. Mounting an expansion tank horizontally would put a lot of stress on the connection and could potentially result in leaks and/or tank failure.
By PexUniverse Customer Service on 12/11/2019 
