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How does an expansion vessel work?


Central heating systems are prevalent in households in the UK. It is almost impossible to come across a modern home with a stable heating system to make the atmosphere of the home comfortable. Living where the temperature drops drastically during peak winter, a heating system becomes the saviour that keeps the home warm and looks after the unlimited hot water supply. An expansion vessel is an integral part of heating systems. In this blog, we ask ourselves how does an expansion vessel work? So, let’s read on to find the answer to this. Found primarily on domestic heating systems, the expansion vessel is also recognized as an expansion tank. 

An expansion vessel maintains the correct pressure level in the entire heating system. This vessel is usually common in combination boilers and contains water and air necessary for maintaining adequate pressure. You must be curious to discover more about the function of an expansion vessel. Stay glued till the end to find the answers to the most commonly-asked questions by users. Alternatively, we would also like to keep you posted about our services. Check out our homepage to read about services such as power flushing in London.

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What happens if the expansion vessel fails?

Failing an expansion vessel does sound nightmarish, but is this a serious issue? How can you deal with a situation when your expansion vessel has failed? Surveys have found that one of the most common reasons behind the failure of an expansion vessel is over-pressurizing. This over-pressurizing occurs when the valves are faulty and the water entering the vessel cannot expand as it should. This situation of over-pressurization can sometimes prove to be catastrophic. Expansion vessel faults are expected mainly in sealed central heating systems.

As the name suggests, the expansion vessel is the tank where the water expands because of heating; as a result, pressure creates. To ensure this pressure does not cross the normal bar, an expansion vessel is responsible for maintaining that. Still feel like you could learn more about how does an expansion vessel work? We’re not done yet! Our team at Boiler Solutions is focused on keeping you up-to-date with blogs and articles about boilers and other home units. So, since we are on the topic of expansion vessels, why not read our blog titled how do I know if my expansion vessel is faulty?

Issues that may crop up

When you suddenly witness simultaneous fluctuations in the pressure gauze, it indicates the malfunctioning of an expansion vessel. An imbalance in pressure leads to overheating of the boiler and eventually causes it to shut down. In this scenario, you will stop getting a hot water supply, and the central heating system won’t work correctly. Pressure swings are a nightmarish scenario and, if not dealt with immediately, may cause significant damage to the system. If you are unaware of the functions of central heating systems, it is wise to appoint a registered Gas Safety engineer. An experienced professional can help you recognize the root cause behind such a failure and deal with it quickly.

Now, you must be curious about the most common reasons behind the failure of an expansion vessel. How can you be extra sure that your expansion vessel is faulty? Here are the three most common reasons behind a failed expansion vessel:

  • There is a rust build-up in your expansion vessel.
  • You must be aware of the water leakage from your expansion tank. If you have a sealed heating system, leaks are infrequent.
  • The filling valves are faulty, and there is an unexpected air leak.

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What pressure should I set my expansion vessel to?

Expansion vessel tanks contain air, and they release pressure when the water flows inside. Inside the expansion tank, the water gets heated and expanded, and to avoid over-pressurization, the vessel compresses and absorbs added pressure. What pressure should be set is one of the most common questions asked by new users. According to experts, the ideal pressure for an expansion vessel is between 1 and 1.5. Hence, they suggest keeping the bar at 1. As the boiler begins to function, the pressure in the expansion vessel slightly fluctuates by 0.5 bar. So, they suggest keeping the bar at 1, which is within the standard limit. If your expansion vessel comes with readings of 12 to 40 psi, then you should set it at 12.

How does a cold water expansion vessel work?

Although the function of a hot water expansion vessel is familiar to people, they always need clarification on the function of a cold water expansion vessel. Isn’t the functioning of expansion vessels the same for hot and cold water? To answer that, the function of cold water systems is almost the same, and the difference lies in heating and cooling, expansion and contraction of water. Almost all cold water expansion vessels have sealed systems. A cold water expansion vessel resembles a cold tank connected to the cooling system.

When the cold water enters the expansion tank, the air is already inside, creating a space for the water to contract. This further helps maintain an average pressure in the system and prevents over-pressurization. We hope this blog helped you get an answer to how does an expansion vessel work? Regarding the opposite, here’s a blog on how hot water circulation pump works. Check it out as well as other informative blogs that you’ll find on our website.