LARGER VIEW of a heating boiler expansion tankAmtrol Extrol®, the Fill-Trol® Expansion Tank
How to troubleshoot, drain, or service & repair the expansion tank on hot water heating systems

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Amtrol / Extrol® internal-bladder heating equipment expansion tank: what is an diaphragm or internal-bladder type expansion tank, how do they work, and how are they installed, adjusted, maintained & repaired?

This article series describes how to identify, inspect, install, repair, or service heating boiler expansion tanks: here we explain the function of expansion tanks on hot water (hydronic) heating systems. We provide a heating system expansion tank Troubleshooting & Repair Guide.

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Amtrol's Adapted Extrol®, the Fill-Trol® Diaphragm-Type Expansion Tank

Amtrol's adapted Extrol Fill-Trol Expansion Tank (C) D Friedman

The expansion tank shown at left looks a lot like the one shown at the top of this article, right? But it's got some added features.

I wish we could push those wires out of the way, but instead, look at that brass valve just above where our red arrow is pointing. That's the adaptation. Amtrol has added a specially designed pressure-reducing valve that will automatically feed water into the heating system as needed.

This is Amtrol's adapted Extrol® tank called the Fill-Trol® diaphragm-type expansion tank.

[Click to enlarge any image]

This tank resembles the simpler Extrol® hydronic expansion tanks but adds an automatic valve that eliminates the need for a separate automatic water-feeder or "fill valve" for the heating system boiler.

So in one package we have the expansion tank (below the red arrow) and an automagic water feeder (at the red arrow).

The whole assembly has been mounted to a tapping on the under-side of the air scoop and all of this is located above the heating boiler (a gas fired unit in this example).

Our sketch shown below, adapted from Amtrol's FillTrol® product literature, illustrates how the FillTrol® valve works to combine an automatic water feed valve for a hydronic heating system with a valve that admits expanding hot water from the system into the expansion tank bladder.

Amtrol's Filltrol(R) automatic fill valve - Amtrol Inc adapted by InspectrAPedia 2014

Separately at WATER FEEDER VALVES, HYDRONIC BOILER we explain the function of pressure-reducer/water feed valves on hydronic (hot water) heating boilers in general. In the case of the Fill-Trol, the valve will put water into the heating system (via its distribution piping) should the pressure fall below 12 psi.

If you go back to look at the photo at the very top of this article you'll see a similar expansion tank, mounted in a similar location, but without this special pressure-reducing water feed valve. That heating system will need a separate automatic (or manual) water feed valve.

Installation of the internal-bladder Amtrol Extrol® expansion tank

Amtrol specifies the expansion tank mounting position in the installation instructions for the Amtrol Extrol Expansion Tank No. 30 (found at the References section of these articles) in text, from which I quote:

Mount tank vertically in downward position only. Ensure the piping can support the entire weight of the tank when full of water.

Amtrol Extrol expansion tank installation schematic, adapted from Extrol (R) installation instructions (C) InspectAPedia

A pre-charged internal-bladder type expansion tank such as the Amtrol Extrol® is installed on the outlet side of the heating boiler between the boiler supply outlet and the heating circulator pump(s) as shown in our adaptations of installation schematics provided by Amtrol. The internal pressure of the bladder tank is set to equal the system fill pressure (eg. 12 psi cold on many systems) and should not need further adjustment.

Atrol Extrol installation schematic adapted fro Extrol (R) installation instructions (C) InspectApedia

Air vent & purger for Amtrol Extrol Tanks?

Reader Question: Does the "Amtrol Extrol Expansion Tank No. 30" need air vent and air purger - Anonymous: 3/3/2014

Reply: Anon: for the operation of the Extrol expansion tank itself an air vent and purger are not required, but for proper functioning of the heating system where the Amtrol Extrol Expansion Tank No. 30 is installed, indeed an air purger and vent are needed. Here is what the company says in the installation instructions for their Extrol expansion tanks:

The EXTROL is installed on the supply-side of the boiler system. Its sealed-in air pre-charge prevents water from entering the tank until the system pressure begins to rise.

As the water temperature rises, water enters the EXTROL. As the system cools, the diaphragm is forced downward. Water is expelled from the EXTROL, back into the heating system.

Although the EXTROL does not have to be installed at the base of an air purger, this installation is recommended to reduce air in the system and provide a compact installation. Some method of air elimination is required to ensure an oxygen-free system. - Extrol® (2014)

See the Extrol installation & operation instructions found at REFERENCES at the end of this article.

Mounting Position for the Amtrol Extrol® expansion tank

Reader question: I have a system 2000 gas fired furnace that has a Extrol 30 that is mounted sideways instead of hanging down. It has waterlogged for a fourth time in the last 20 years and about four years ago was the last time until now. Does the tank being mounted horizontally instead of vertically have an effect on the life of the bladder? I don't remember ever having to replace one in any house I lived in until I moved in here. Rick Bouchard 3/25/2014


The Amtrol company's installation instructions for the Extrol 30 does not explicitly mention horizontal vs. vertical mounting position for the device, but the installation instructions do include a sketch showing the unit in a vertical position.

The instructions also include this line "Do not place the EXTROL on a dead-end pipe. Air can collect in the EXTROL, causing internal corrosion and possible leakage." Which I take to warn you that *any* installation that might allow air to collect in the device could cause corrosion and leakage. That is, in my opinion, precisely the risk that you might face if your unit is mounted horizontally.

A review of both product brochures and installation literature all show the expansion tank in the positions shown in Amtrol's Extrol sketches adapted above.

You can contact the company directly as well both for warranty claims or to double check the tank mount position. Note that the warranty will not cover damage or failure attributed to improper installation of the device.

What goes wrong with internal bladder type heating system expansion tanks?

Normally these internal-bladder expansion tanks never need adjustment of their air pressure. But as we noted near the start of this article, if the internal bladder of the tank ruptures the tank may eventually become waterlogged. If the expansion tank is a model that includes an air pressure adjustment valve on the tank, you may find that a burst internal tank bladder means you will find water leaking out of the air charge valve, or water will squirt out of the valve if its center pin is depressed.

If the internal bladder type expansion tank such as the Amtrol® Adapted Extrol-R, the Fill-Trol-R Diaphragm-Type Expansion Tank is not a model that can be rebuilt with a new internal bladder, the tank will need to be replaced.

Here are some additional notes warnings quoted from Amtrol Inc.'s installation instructions for the company's Extrol® hydronic diaphragm expansion tanks in-line & SX series. The first 7 notes are of particular interest to the installer.

Amtrol Extrol Models #15 through #90 come with a 5 year warranty. All other EXTROL models come with a 1 year warranty. *

Question: adusting the pressure on an Amtrol Fill-Trol expansion tank

(Dec 7, 2014) John said:
My oil boiler has a fill-trol model 110 with an automatic valve on it and the system has been turned off for 1 year and I notice that water pressure is 40psi and is popping off at the pressure valve.I can hear water coming from my main water line so I turned it off.Can I clean the automatic valve because the water is bypassing it. Could the spring be stuck or is the tank not pushing on the valve to shut it off.Thanks


John 40 psi is much too high - I would look for a problem with the pressure-reducer water feeder mechanism. Indeed your model, as described by Amtrol, "The AMTROL FILL-TROL® system consists of a specially adapted EXTROL® pre-pressurized, diaphragm-type expansion tank, and the FILL-TROL, a specially designed, automatic, fill valve."

The problem could be something as trivial as debris on a valve seat. There is a screen in the valve that is intended to be removed for cleaning.

The whole FillTrol valve assembly can be removed for cleaning but depending on what control valves were installed on your heating system you may have to drain part or all of the system to remove the expansion tank and fill valve assembly. And I would not try such a repair before checking the product's maintenance instructions or asking the company for advice, AND I would not begin such a repair without having a repair kit of parts on hand - typically o-rings, gaskets, etc.

I would give the company's tech support a call at 401-884-6300

The problem could also be a failure at your building water pressure regualtor subjecting the whole building to abnormally high pressure.

Question: failure at the Amtrol Fill-Trol valve allowed boiler to go dry?

(Mar 8, 2015) Mike said:
Would my amtrol fill-troll supply valve system not functioning properly cause my boiler to go dry. I don't see any signs of any leakage. Where would the water go in the closed system
flag like



Almost certainly in a hydronic heating system (hot water heat) if the boiler has gone dry we have a double fault: a leak somewhere AND the water feeder was not replacing lost water (or there was no automatic water feeder, as is the case on some old systems).

So most likely the leak is somewhere not obvious such as in a crawl space or under a slab. If you have heating pipes running under a slab or for that matter anywhere, if you re-fill the system and fire up the boiler (you'll have to bleed out or remove air to get it working) you might get help finding the leak using IR or thermal scanning to look for the heat of leaking hot boiler-water.

Article Series Contents


Continue reading at AMTROL EXTROL® FILL-TROL® FAQs or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see EXPANSION TANK DIAGNOSTIC FAQs - more questions & answers about boiler expansion tanks or "boiler compression tanks"

Or see EXPANSION TANKS, BOILERS - topic home

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