Hot Water Expansion Tank
Installation tips

Hot water expansion tank is the safety device that is used in closed loop heating systems, to take the expanded hot water and therefore prevent from leaking in plumbing system and heater malfunction.


Depends on the capacity of the heater, the right expansion vessel size should be used so it can safely store thermal expansion.

How it works

When the heater is running, it produces a hot water. The pressure in the heating system rises, expanding the volume of water in your plumbing system. The extra volume has to go somewhere, and since the system is closed, expansion unit has to be used.

Otherwise, if you don't install this device the high pressure in plumbing and the heating unit can cause leaks or the heater failure.

More serious problems may occur with the gas heaters, where internal flues may collapse causing the release of carbon monoxide into your home.

expansion tankExpansion tank is a simple and small device. It is container that is divided into two sections and divided by a rubber diaphragm. One side of the tank contains water and is connected to the plumbing system, while the other side contains an air under pressure.

When the extra hot water has to be taken, water enters into the expansion device and moving the diaphragm, which is compressing the air out and providing space for additional water.

Expansion vessel in residential heating systems has to meet regulations and to be able to accommodate the heater size. When looking for the expansion vessel to buy, size is important, and it depends on your heater capacity and water pressure in your house plumbing.

expansion tank for water heating

FLEXCON 8.5 Expansion Tank


emergency plumber

How to install the Expansion Tank

An expansion vessel has to be installed on the cold water supply line. Follow the instructions provided by the manufacturer. It is very simple plumbing work of 30 min. installation, with basic tools like Teflon tape and wrench.

When installing the unit, the heater, water line, gas and electricity has to be turned off to make the installation easier and safer.

The best location is on the horizontal supply line and above the pipe, close to the heater and securely fastened to the wall or any other support.

Tee fitting can be used where one end will be connected to the threaded part on the expansion vessel. Use Teflon tape around the proper end and pipe wrench to tighten it to the heater plumbing line.


How to replace Expansion Vessel

The expansion vessel must be properly charged with the air in order to function properly. If for any reason you see that pressure relief valve on water heater is spurting water, or there is an extreme pressure on gauge, or expansion vessel is full of hot water, than you are experiencing unit malfunction.

If expansion tank has to be replaced, follow the steps below:

  • Turn off your heater and let the hot water cools.

  • Shut off the cold water supply to the heater.

  • If you have to drain a system, do so.

  • Unscrew the old heater expansion tank.

  • Put the new expansion unit on the same spot.

  • Use Teflon and pipe wrench to securely tight the unit.

  • Turn the water on and check for leaking.

  • Turn the electricity and gas supply on.

  • Turn the heater on and check the pressure and hot water temperature to see is your expansion tank working properly.


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