Bind – Gas Safe Registered Boiler Engineers, Somerset & Wiltshire

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If you have a system or combi boiler losing pressure but no leaks, you may be wondering what is causing this problem. Low boiler pressure can affect the performance and efficiency of your boiler, and make it harder to heat your home. Low boiler pressure might even point to something more serious lurking beneath the surface, like a leak or a damaged component.

In this guide, we will explain why your boiler loses pressure and what causes this problem in the first place.


The role of the expansion vessel

The expansion vessel is a key part of your combi boiler system. It is a steel container that has a rubber membrane inside, separating the water from the air (or sometimes nitrogen). The expansion vessel allows the water to expand and contract as it heats up and cools down, without affecting the pressure of the system.

What happens when the expansion vessel is faulty?

When the expansion vessel is faulty, it can cause the pressure of your boiler to fluctuate. When your heating is on, the water will expand and push against the air in the expansion vessel. If the air is not compressed enough, or if the membrane is damaged, the water will force its way into the pressure relief valve. This valve is designed to release excess water when the pressure reaches 3 bar, to prevent damage to your boiler.

When your heating is off, the water will contract and pull back from the pressure relief valve. This will cause the pressure of your boiler to drop, and you may need to refill it with water. If this happens frequently, your boiler will go into fault mode and stop working.

This is one of the most common reasons for a combi boiler losing pressure but no leaks. Adding fresh water to your system all the time can cause corrosion and rust, which can damage your pipes and radiators.

How can you tell if your expansion vessel is faulty?

The easiest way to tell if your expansion vessel is faulty is to check the pressure gauge on your boiler. If the pressure rises when your heating is on, and drops when your heating is off, you may have a problem with your expansion vessel. You can also look for signs of water leakage from the pressure relief valve, which is usually located on the outside wall of your boiler. If you see water dripping or a wet patch on the wall, you need to get your expansion vessel fixed as soon as possible.

What are some other causes of a combi boiler losing pressure but no leaks?

There are some other possible causes of combi boiler losing pressure but no leaks, such as:

  • A cracked or corroded heat exchanger can allow water to escape from your boiler into other parts of your system.
  • A faulty pressure gauge or sensor can give inaccurate readings of your boiler pressure.

If you suspect any of these issues, you should contact a local gas-safe engineer to inspect and repair your boiler as soon as possible.


Contact Bind – Gas Safe Boiler Engineers, Somerset & Wiltshire

We are experts in all aspects of boiler installation, repair, and maintenance. Bind’s local gas boiler engineers can help you diagnose and fix any problem with your boiler quickly and safely. We offer free quotes and competitive prices for our home heating services.

We also offer some amazing new boiler deals, after-sales boiler servicing and system checks too!


Contact us:
[email protected]
01985 800222