Replacing an Expansion Tank

What is the purpose of an expansion tank for heating?

There are several types of expansion tanks:

• The boiler expansion tank: inside a boiler, there is an expansion tank that absorbs the high pressure from the heating circuit before it moves into the boiler's parts. With its flexible membrane, the heating expansion tank protects the rest of the system.
• The external expansion tank: this is often used for floor-standing boilers, serving the same purpose as the wall-mounted boiler that includes an integrated expansion tank.
• The sanitary expansion tank: this time, the expansion tank does not absorb pressure from the heating circuit moving from the boiler to the radiators or underfloor heating. When your boiler has a domestic hot water circuit, the expansion tank for hot water prevents excessive pressure in your home's plumbing. Too much pressure could damage your faucets and pipes.

The tools to change an expansion tank

To replace your expansion tank, you will need:

• A wrench to remove the old tank
• A pressure gauge
• Rags
• A new expansion tank

How to change an expansion tank?

POLO:
To regulate the pressure in the boiler, it has an expansion tank (7 liters, 8 liters, 10 liters, ...). Always replace a tank with another that has at least the same volume; if there’s space, you can use a larger one, which isn’t an issue.

POLO:
Inside, there is a membrane that withstands pressure each time it is used.

THIERRY:
This makes the expansion tank a wear item that you may need to replace.

THIERRY:
First, you will need to drain the system. Do this in the simplest way according to your setup. Use rags for leaks. Remember to install a check valve on your system, which will help avoid draining next time.

POLO:
Yes, but how?

THIERRY:
You can use a valve like this one.

THIERRY:
Bend your legs well to avoid injury!

POLO:
Alright, I'll let you handle it then. Be careful with your back, or you’ll be out again.

THIERRY:
Now, next step: it’s time to install the new expansion tank.

POLO:
Okay, let’s go!

THIERRY:
Check the pressure of the tank to be installed, around 0.8 bar. If it’s not, you will need to use a pump for the expansion tank.

POLO:
0.8, perfect, that’s what we need!

THIERRY:
In that case, you can install the expansion tank on the piping. Use a flexible line because we’re not at the right height, along with a valve to facilitate the connection. Remember the seals.

POLO:
No problem. Now all that’s left is to fill the system, right?

THIERRY:
That’s it, very good work, Polo. Remember to check for any leaks after the job.

THIERRY:
To avoid changing the expansion tank again, make sure to maintain your system. Sludge in the piping damages the parts of your boiler. That’s why I recommend descaling and installing a magnetic filter on your system.