The expansion tank is a crucial component in a boiler. It ensures the proper functioning of the system by maintaining a constant pressure level.
When this component is defective, it causes certain heating failures. Its replacement then becomes unavoidable.
If you want to get more information on this subject, this article can serve as a guide. But before going into details, it is important to summarize the essentials to know about an expansion tank.
📋 The essentials at a glance: Personally, I consider that changing an expansion tank is an operation accessible in 70% of cases with the right tools. I have often noticed that most boiler pressure-related breakdowns come from this part. By following a rigorous method, you can save between 80 and 200 euros in labor costs. It is a technical intervention but perfectly doable as a DIY project.
What is the main role of an expansion tank?
🌍 Did you know? A defective expansion tank can increase your boiler’s energy consumption by up to 15% due to repeated heating cycles.
The expansion tank is primarily a reservoir of small or large size. Its capacity varies according to the volume of water in the system and the power of the boiler.
If the tank is reserved for heating, it is red in color. On the other hand, a white one is intended for the domestic hot water installation.
In a circular, flat, oval, or rectangular shape, this part consists of two inlets. One is dedicated to the hydraulic part and the other to the gas.
It performs two important functions. The expansion tank allows, on the one hand, to maintain a constant pressure in the system throughout the heating cycle. And on the other hand, it preserves the water level in the circuit.
It should be noted that water expands during heating. As a result, it can take up more space. To avoid overflow, the surplus will be directed into the expansion tank.
The latter also serves to accumulate the coolant. To maintain the level, it must be filled. This also helps prevent engine overheating.
🗣️ My experience: I replaced an expansion tank in an apartment in Lyon in the middle of winter, after repeated pressure drops. The part cost me 45 euros and I took about 1h30 without prior experience. Since then, no more heating problems. Lesson learned: never ignore unstable pressure, it is often the first sign.
⚠️ Classic trap
Many think that simply reinflating the expansion vessel is enough to fix the problem. In reality, if the membrane is pierced, it is useless and the fault quickly returns.
How to know if my boiler’s expansion vessel is dead?
When you are not familiar with the technical field, many questions come to mind. How to check the state of the plumbing? Otherwise, how to identify a maladjusted or damaged expansion vessel?
Sometimes, this last issue must be dealt with urgently, especially since the vessel is among the essential components of the central heating. So if you want to enjoy it for a long time, you need to have the reflex to check it from time to time.
To do this, it is advised to use a pressure gauge to check the pressure. When 0 bar is displayed, you must first inflate the expansion vessel until you get a good pressure. Then, test it and check if the tank maintains it or not.
Besides that, a water leak is among the signs revealing a defective expansion vessel. The bladder might be porous or pierced. In this case, replacement is the only solution.
As a rule, the boiler automatically switches to safety mode when it detects a pressure problem. Also, when the circuit frequently lacks water and refilling happens quickly, this should alert you to a vessel in poor condition.
In any case, nothing beats consulting a heating engineer. With their skills and experience, they can determine the condition of the expansion vessel.
If you also want to know how to bleed a heated floor, this same professional can help you.
💡 Practical tip
Remember to check the circuit pressure after installation. It should generally be between 1 and 1.5 bar for optimal operation.
When should the expansion vessel of a boiler be changed?
🍀 Advantages
Labor cost savings
Quick intervention
Immediate performance improvement
🔻 Limitations
Technical handling
Risk of error without experience
Over the years, the expansion vessel can undergo countless stresses related to corrosion, temperature, and pressure.
No matter the model, this part generally has a lifespan of 8 years. Even if you regularly maintain it, it must be replaced once this limit is reached.
When this approaches, the vessel gradually starts to lose its performance. Its filling happens very quickly. To avoid reaching this stage, it is better to change it once and for all.
Some signs can also warn you of its malfunction, which requires its replacement. The boiler for example goes into safety mode even though it is recent. Otherwise, the pressure keeps dropping, even after topping up.
In all these situations, it is urgent to uninstall the old expansion vessel and use new equipment.
| Type | Capacity (L) | Price (€) | Lifespan (years) |
|---|---|---|---|
| Standard | 8 | 30 | 5 |
| Medium | 12 | 50 | 7 |
| Large capacity | 18 | 80 | 8 |
| Premium | 25 | 120 | 10 |
Where to place an expansion vessel on a boiler?
Its incorrect placement can cause certain operational anomalies as well as severe corrosion. Its position should therefore not be chosen at random.
This part should normally be integrated into the boiler. It must be connected to the return of the heating device. To limit pressure losses, make sure its location is as close as possible to the boiler.
The vessel must also be located at the correct height. You can adjust it to the same alignment as the top part of the installation. Also, position it above the circulator.
If you are not sure, it is best to call a professional. If you don’t know who to contact for boiler maintenance in Bordeaux, Nice or Paris, do not hesitate to check online. In just a few clicks, you will get a list of technicians in your area.
Where does the water from the expansion vessel go?
The expansion vessel is very useful on any heating system, especially on the domestic hot water circuit.
No matter the system, its mission is to collect the excess water caused by the expansion of water during heating.
In practice, this tank is filled with air in its initial position. When the water starts to heat and expand, it goes directly into the vessel while compressing the air inside. This excess water will cool down inside the vessel.
If you plan to install it, start by determining the installation location. It is a strategic place ensuring the complete operation of the heating system.
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