Why does my boiler keep losing pressure?

Why does my boiler keep losing pressure?
17 January 2023
Why does my boiler keep losing pressure?
A pressure gauge on a gas-fired boilerA pressure gauge on a gas-fired boiler

If you've got a hot water central heating system then your boiler is possibly the most important item in your home. For your boiler to operate as efficiently as it possibly can, the water it heats and circulates around your pipes and radiators needs to be at a certain pressure. Too high and your boiler runs the risk of shutting down completely to protect the system, too low and you run the risk of some of your radiators not getting hot.

Like many things, low boiler pressure is not something many of us think of until it adversely affects us, but in this article we'll look at what the symptoms of low boiler pressure are, what might be causing them and how you can fix it.

Symptoms of low boiler pressure

  • Your radiators won't get hot
  • You don't have hot water

The above two symptoms are the most common things you'll notice when your boiler pressure has dropped too low. When this happens, the pressure simply isn't high enough to push the hot water around your home.

Water pressure is measured in 'bars' and If you look at the gauge on the front of your boiler, any reading below 1 bar means you have boiler pressure that is too low. 

Causes of low boiler pressure

  • There might be a small leak

When there is a large leak in a central heating system, you tend to notice it pretty quickly - an increasingly-large discolouration in a ceiling or a wet patch on a floor. With small leaks however, they are often much less subtle and will only be noticed if you're heating system struggles to get hot and the pressure on your boiler starts to drop below 1 bar. 

You should have a look around your home for any spots of moisture or damp patches, for example around the boiler, radiator pipes, dark areas on walls, ceilings or floors. It might be as simple as a radiator valve needing to be tightened, but it could be something uch more serious, including inside the boiler itself, so it's recommended that you call a Gas Safe Registered heating engineer to come and identify the problem. Small leaks often turn into big leaks, so getting to the bottom of the problem quickly will usually spare you more serious pain and expense down the road.


  • There's air trapped in your radiators

If your radiators haven't been bled for a long time, then it could be the case that air has worked its way into the central heating system and got trapped at the top of some radiators. This can sometimes be due to a leak, but also just a natural occurance as a result of long periods of use. If your boiler pressure is below 1 bar and your radiators feel warm at the bottom and cold at the top, bleeding out the air may well solve the issue.

In the video below, James the professional plumber, shows you how to bleed your radiators.

What should boiler pressure be?

A healthy boiler pressure should be somewhere between 1 - 2 bars. Looking at the gauge on your will show you what your boiler pressure is currently.

When the boiler is on, it will naturally start to increase and should reach a pressure of somewhere between 1.5 - 2. When the boilers goes off and starts to cool down, it will naturally start to lower and should read between 1 - 1.5 bars.

If it keeps dropping below 1 bar then there is clearly an issue that needs addressing, At the other end of the scale, if the boiler pressure rises above 2.5 bar and goes into the red when switched on, your boiler pressure is too high and should be switched off and investigated.

How to increase/re-pressurise your boiler pressure

Only do the following if you are comfortable with a bit of plumber and DIY tasks, otherwise, get in a professional who will be able to do it and possibly identify any other issues that need addressing.

1. Switch off your boiler and allow your heating system to cool down

2. Find your filling loop, which is normally located under your boiler. If it isn't, look in your boiler's manual to try and work out where it is.

3. At the filling loop, you will see two pipes with valves or handles. With an eye on your boiler's pressure gauge, open up these valves to allow water into the system.

4. You should notice your boiler pressure increase and can turn off both valves when the pressure reaches 1½ (halfway between 1 and 2 bars).

5. Wait a few minutes and see if your boiler pressure stays between 1 and 2 bars on the gauge. Also have a quick look around your radiators and pipes to check for any leaks.

6. If everything looks good then switch your boiler on again and check that your radiators are getting hot.

7. After using your heating, turn your boiler off again and check that the pressure hasn't dropped again.

Radiators at TradeRadiators.com

Once you've got your boiler up and running again, you might want to consider some nice new radiators to ensure your home is getting as warm as possible while using the least amount of energy. 

Trade Radiators’ own brand of radiators, known as Trade Direct, encompasses all of the positive qualities of Trade Radiators. Made from high-quality materials and specifically designed to complement all types of interiors, the brand is the most versatile on the site. Prevalent in all of the site’s ranges, Trade Direct radiators and towel rails provide customers with high-quality radiators at an affordable price. Whether you are looking to kit out your whole home or are looking for a statement piece, the diverse range of radiators and towel rails in the Trade Direct brand ensures that you will find exactly what you are looking for. 

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