Without expansion vessels, your home's heating system would not be able to maintain a constant pressure. They are essential for closed-water systems like combi boilers.

Some people may not know what an expansion vessel is, or what it does. It’s a crucial part of your heating system that allows it to maintain a constant pressure. If you have a closed-water heating system in your home, such as a combi boiler, you will have an expansion vessel.

It helps maintain water pressure in a household. Over time, the expansion vessel can become depleted, which can lead to decreased water pressure. If you notice your water pressure declining, it may be time to recharge your expansion vessel. Fortunately, by following this handy step-by-step guide, this is a process that you can do yourself. 

This guide will answer the following questions:

  • What is an Expansion Vessel?
  • How Does an Expansion Vessel Work?
  • How to Locate the Expansion Vessel?
  • How to Check the Pre-charge Pressure of an Expansion Vessel?
  • How to Charge an Expansion Vessel?


What is an Expansion Vessel?

An expansion vessel, also known as an expansion tank, is a type of pressure vessel that is found in most domestic pressurised heating systems. They are designed to hold extra fluid in a system so that when the fluid expands (due to heat), it can do so without damaging the system.

Expansion vessels are typically made from steel or other durable materials, and they can vary in size depending on the application. They are an important part of many heating systems and play a vital role in ensuring the safety and longevity of the system.

How Does an Expansion Vessel Work?

An expansion vessel is a crucial component in any heating system that uses a boiler. It helps to ensure the boiler can operate safely and efficiently by providing a space for the expansion of water as it is heated. Without an expansion vessel, the pressure in the boiler could become too high and cause the boiler to malfunction or even explode.

The expansion vessel is typically filled with air and nitrogen which provides a cushion for the expanded water. As the water expands, it increases the pressure within the vessel. This increase in pressure is what protects the boiler from becoming over-pressurized.

How to Locate the Expansion Vessel?

If you have a boiler in your home, then you likely have an expansion vessel as well. If something goes wrong with the expansion vessel, it can cause serious problems with your boiler. That's why it's important to know how to locate the expansion vessel and what to do if something goes wrong with it.

The expansion vessel is usually located near the boiler, sometimes even inside the boiler casing. If you're not sure where it is, or can’t find it, you can ask your heating contractor, or a qualified heating engineer for help.

Once you've located the expansion vessel, it's important to check it regularly to make sure that it's in good working order. You should also know what to do if something goes wrong with the expansion vessel.

How to Check the Pre-charge Pressure of an Expansion Vessel?

Instructions on how to check the pre-charge pressure should be noted on the expansion vessel itself. It's important to make sure the expansion vessel is not over-inflated, as this can cause damage.

Have you ever had a problem with your expansion vessel? We'll show you how to check the pre-charge pressure of an expansion vessel so that when it loses air over time, it can still operate smoothly.

To ensure that you have measured the correct pre-charge pressure for your expansion vessel, it's important to use either a tire gauge or some other device capable of measuring pressures. The expansion vessel should have a valve on it that says "pressure relief valve" or its abbreviated form “PRV.” The valve pointing perpendicular to the expansion vessel is essential for proper operation. Next, place the tire gauge on top of your gas tank and press down. The reading from this device will let you know how much pressure is currently in front or behind what's needed for proper inflation.

If the Expansion Vessel has lost pressure: you will need to add air to it.

To ensure that your expansion vessel is working optimally, you will need an air compressor with a nozzle fitted onto the valves. Attach it and turn on as usual, until pre-charge pressure has been reached correctly

The idea of checking the pressure in your expansion vessel is simple and straightforward, but it's an important part to keeping any boiler running smoothly. By regularly doing this task, you can make sure that there will always be enough steam or hot water available for all purposes no matter what time a crisis strikes!

How to charge an Expansion Vessel?

If you're looking to recharge your expansion tank for the boiler heating system in your home, then this task won't be too difficult. However it will require some tools and time from start-to-finish so allow yourself several hours to get this task done.

1. What does it mean to recharge an expansion vessel?

When the water in your expansion tank takes up too much space, it can cause air pressure to change. To recharge an expandable unit with proper levels again means removing some excess liquid and replacing that which was removed. This process is known as "recharging."

2. Inspecting the system

Make sure you have a good inspection of your boiler unit before recharging it. Check to see that all fittings are tight and there are no leaks anywhere on the machine, because if not then those cracks will only get worse when pressure builds up again during use.

3. Draining the tank

Start by turning off your boiler’s switch and close the pipe valve that connects from the water tank to the expansion tank. Your boiler may already have a hose attached to the expansion tank, if not you can attach a standard garden hose. Alternatively, you can place a bucket under the drain.

In order to empty out your water tank, open the valve and either loosen it or remove the six-sided connector. Loosen any screws that hold this part in place with an adjustable wrench. If you do not drain the tank completely then it will not properly recharge.

4. Recharge the expansion tank

Make sure there is no water left in the expansion tank before removing any hoses or closing valves. If all the water has been drained, reattach all of your connections, including the six-sided connector, and make adjustments as needed so everything seals back up tightly!

When you turn on the water valve between your tank and expansion pipes, make sure to listen for running water sounds. When you no longer hear water flowing, then check the air pressure by reading the pressure gauge. The optimum PSI should be between 10 and 12.

Just like that you have successfully recharged an expansion vessel. If you have trouble with your boiler, contact a professional, as there could be problems you didn’t foresee that are out of your control. Or, your boiler may need replacing completely.