How To Reduce Boiler Pressure

Practically everyone owns a boiler, but many people don’t quite understand how they work. Boilers moderate central heating systems using water and the pressure must be just right in order for them to function appropriately. Keeping the pressure at an optimal level is both energy efficient and cost effective.

However, sometimes the pressure will rise above this optimal level, causing unwanted issues. The following article explains how to reduce boiler pressure back to normal when this happens.

What is Boiler Pressure?

In the simplest terms, boiler pressure refers to the balance between water and air in your central heating system. This is not to be confused with the water pressure related with running tap water.
For your boiler to work as intended, the boiler pressure must be at an optimal level, meaning not too low but at the same time not too high. Low boiler pressure could prevent your central heating system from working by completely cutting it off. On the other hand, high boiler pressure overloads your system and causes it to fail.

What is the Optimum Boiler Pressure?

Whilst there’s no definitive answer, most boilers will perform between 1 and 2 bar. This equates to between 14 and 30 pounds per square inch (PSI). Your boiler will have a pressure gauge that shows this figure on the control panel – usually marking the pressure out of a maximum of 4 bars. If you need further assistance or confirmation of this, refer to your boiler’s user manual.

What Causes High Boiler Pressure?

High boiler pressure can have a variety of causes. But before getting into those, it’s important to note that your boiler pressure will naturally rise whenever your heating or hot water is in use. This will cause a spike in the reading but there’s no need to panic because it’s normal. That being said, it shouldn’t rise above 2.5 bar. If it continuously stays between 2.5 and 4 bar, you may have a problem.

One of the most common causes of high boiler pressure is an excessive amount of water in the system. This usually occurs after adjusting the boiler pressure from a very low level. It may be the case that the valve or filling loop used to pump water into your boiler was mistakenly left open. This is normally located at the bottom of your boiler and you need to check that is tightly closed.

Faulty parts, such as a leaky valve, can also cause high boiler pressure. If you’re struggling to identify the cause, call your warranty provider to send a qualified gas engineer out for inspection.

How to Lower Your Boiler Pressure

Thankfully, lowering your boiler pressure is fairly straightforward. You’ll just need to bleed your radiators. This reduces the pressure in your central heating system, which consequently lowers your boiler pressure.

First, you’ll need a radiator key, which you can purchase from your local hardware store if you don’t already own one. Before bleeding the radiator, make sure that the boiler is cold. It’s a safety measure that ensures you don’t get burnt by scorching hot water.

From there, locate the release valve on your radiator, which is usually found on the top of the unit. Then using your radiator key, turn the valve to slowly release air from the radiator. Water will also start to leak from the unit, so it’s important to have a small container and a cloth or towel nearby to prevent a wet floor.

When you’re sure that you’ve successfully completed the bleeding process and there is no more air or liquid being discharged from the radiator you will notice that your boiler pressure will start to reduce back to normal.

Bleeding My Radiator Didn’t Work, What Now?

If bleeding your radiator didn’t work, there’s probably another issue at fault. You may have a problem with either your pressure gauge or another internal component, such as the expansion vessel. This task should be left to a qualified engineer to ensure the job is carried out correctly. For this, head over to the Gas Safe Register. It is an official register of all verified engineers in the UK, Isle of Man and Guernsey that can legally carry out gas work. A quick browse of the site will help you to easily find a qualified engineer in your local area.

It is paramount that you do not attempt to carry out any maintenance work on your boiler without the help of a professional. You won’t be covered by your warranty and risk jeopardising your own safety. In addition to this, it’s also illegal to use any gas appliance that is thought to be unsafe. As such, it’s better to err on the side of caution than be sorry later.


As can be seen, reducing boiler pressure isn’t as complicated as it seems if you know what to look for. It’s good practice to check your control panel for the pressure reading every once in a while. If it stays above 2.5 bar, it could cause boiler failure.

The first point of order in such cases is to check that the boiler valve or filling loop is tightly sealed, as this is a common cause of high boiler pressure. Thereafter, bleed your radiator to reduce the pressure back to its optimal level for normal performance. If this doesn’t work, enlist the help a of Gas Safe Registered engineer. They will identify the root cause and fix the pressure issue safely and correctly.