Why Does My Boiler Keep Losing Pressure?

Find out why your boiler may be losing pressure with our list of potential causes.
Written By: Richard Morgan | Updated:
Boiler Losing Pressure
Richard Morgan/DIY Works

One of the most common issues that most people have with their boiler is the fact that it keeps losing pressure. When this happens, the boiler is far less efficient, resulting in the lack of hot water and warmth from your radiators. However, unlike other boiler problems, discovering why a boiler is losing pressure is relatively easy to diagnose.

If you are experiencing a boiler that keeps losing its pressure, below are some potential causes and how to fix them.

Why Is My Boiler Losing Pressure?

1. Leaks In The System

By far the most common cause of a boiler losing pressure is that there is a leak in the system. This can be a leak anywhere in your pipework that could be located under the floor or even within a wall.

Unless you have had work in your home recently, locating the leak can be quite difficult. Therefore, you will need to trace the pipework around your home and check each joint and bend of the pipework where the seals may have failed.

However, you may also want to look for any damp spots around your home before tracing the pipework, as this may be a significant clue to where the leak is. Once the leak is found, you will need to reseal it or, in the worst case, re-pipe the system.

2. Leak Inside Of The Boiler

Leaks from within the boiler are less common, but many of the components have the potential to leak, which can be caused by old age and corrosion. If this is the case, you will be able to see any of the leaks by removing the cover of the boiler and looking for any signs of water. Depending upon whether there is a leak or not, you may wish to replace the boiler altogether if it’s a relatively old system.

3. Result Of Bleeding A Radiator

If you have recently had a plumber work on your central heating, they may have bled the radiators.

If this is the case, it may have caused your boiler pressure to drop as the collected air has escaped during the process.

Luckily, this isn’t an issue itself, and you can repressurise the system. However, if your boiler keeps losing pressure, the fact that you bled your radiators isn’t the issue, and there may be a problem elsewhere.

4. Faulty Pressure Relief Valve

The purpose of a pressure relief valve is to allow excess pressure out of the system. However, when they fail, this can lead to pressure leaving the system when you don’t want it to, thus causing a boiler to lose pressure.

5. Faulty Radiator Valves

Similar to the leaks within the pipework, a leak can be caused by a faulty radiator valve, which will drip down the pipe. This is a much cheaper repair than a leak within the pipework, and you can replace it with brand-new thermostatic radiator valves or even upgrade it to use one of the latest smart radiator valves.

6. The Pressure Gauge Is Faulty

Although rare, the boiler’s pressure gauge may be faulty. Therefore, no matter how much water you add to the system, the gauge won’t react to the changes. If this is the case, you shouldn’t continue to add water because you don’t want too much pressure within your boiler, as this can lead to further issues.


Depending upon the severity of the cause of a boiler losing pressure will determine whether you need to call a boiler engineer or not. Regardless of the cause, you shouldn’t ignore it because the problem will only get worse and cause more issues further down the line. For example, the constant wear and tear upon the boiler losing pressure or even the leak getting worse and causing damp issues inside your home can be an expensive fix.

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