James Elston

James Elston

Published March 27, 2024

High boiler pressure will cause your boiler to leak water and potentially damage the internal components. It will also negatively affect your boiler’s energy efficiency and general performance. In this guide, we will help you understand what causes high pressure in the first place.

Next, we will tackle what you can do to lower your boiler pressure yourself. This will allow you to prevent leaks or damage to your boiler. Finally, we will discuss what immediate dangers a boiler under high pressure presents and give you the steps to prevent future pressure problems.

What Causes High Boiler Pressure

High boiler pressure is caused when something upsets the natural pressure balance within your boiler and central heating system. The ideal boiler pressure is between 1 and 1.5 bar, indicated by the green zone on your boiler pressure gauge.

If your boiler pressure indicator is in the red zone, the pressure is too high.

 Let’s look at some of the common causes of high pressure in your boiler.

The system has too much water

If your boiler water is overfilled, it will raise the interior pressure. An overfilled boiler could be related to any recent work that you had done on your boiler or central heating system.

If you had any repairs done on the boiler, the attending technician may have overfilled the boiler during re-pressurisation. If the filling loop taps that are used to refill the boiler are left open, it will also cause your boiler to be overfilled.

If you had any radiators replaced or redecorated, the boiler may have been overfilled after they were reconnected. This will make the boiler pressure too high.

If that is the case, you may be able to resolve the issue by bleeding the radiators or checking the filling loop taps. We will discuss how you can check and resolve this in more detail below.

There is a faulty expansion vessel

The expansion vessel is located inside your boiler. This vessel manages pressure fluctuations within the boiler during normal operation.

As the temperature increases or decreases, the pressure will rise and fall in response. A faulty expansion vessel will cause the pressure to increase beyond normal operating levels.

Conversely, a faulty expansion vessel can also be responsible for low boiler pressure.

This is a problem that only a boiler technician can diagnose and resolve.

Blocked pipework

Your boiler and central heating system’s pipework can become blocked, making the boiler pressure too high. Blocked pipework is the result of a buildup of debris or limescale in the pipes.

To fix blocked pipework, you need to contact a boiler technician. They will perform a flush of your system which will clean out any debris that has accumulated within it.

You have a faulty pressure release valve

The pressure release valve is a safety device that allows the boiler to vent high-pressure buildup. If this device malfunctions, the boiler will not be able to vent water or steam when the pressure is too high.

The pressure relief valve will need to be inspected and replaced by a trained professional. We will discuss the pressure relief valve more in our section on how to fix your boiler pressure.

Pressure gauge or pressure sensor issues

If your pressure gauge or pressure sensors are faulty, they may give unreliable boiler water pressure readings. Generally, a mechanical gauge would be more accurate and reliable than a digital gauge.

If you suspect that your gauge or sensors are not giving you correct readings, it’s essential to get a boiler technician on-site. They can source and replace these faulty parts. It is essential to identify high or low pressure within your system accurately.

Boiler age

The average lifespan of a boiler in the UK is 10 to 15 years. While you can troubleshoot and resolve any of the issues we have mentioned, it may just be time to replace your tired boiler. As unsatisfying as it is to hear, sometimes your boiler pressure is too high because the entire system is too old.

When a boiler is nearing a decade in age, it can start costing you more money in maintenance than just replacing the unit outright.

If you think it is time for a new unit, visit Eco Happy. You will find the best prices on replacement boilers and installation specialists in your area.

How Do I Lower My Boiler Pressure?

To lower your boiler pressure, you need to release water from your boiler system or air from your central heating system.

Let’s look at the ways you can manually reduce boiler pressure to safe levels and prevent leaks or boiler damage.

Bleed radiators

Bleeding radiators means opening up a valve on your radiator to let out trapped air or excess water. Fortunately, it is a simple process that you can do yourself.

  • To start, you will need your radiator key, a bucket and a towel.
  • A radiator with air trapped can be identified by gurgling sounds or cold spots. This is due to hot water not flowing properly in the heating system, as air is trapped and blocking the water.
  • Switch off your heating and let the radiators cool down to prevent burning yourself on hot water that will come out during the bleeding.
  • Locate the radiator valve and slot the radiator key in.
  • Set your bucket below the valve to catch water that escapes while releasing the air.
  • Slowly turn the radiator key in an anti-clockwise motion to open the valve and release pressure.
  • Keep the valve open until all the air is out and water is running smoothly from the valve.
  • Close the radiator valve and switch your heating back on.
  • Monitor your boiler’s pressure gauge to check if the water pressure stabilises.

Close your filling loop

Filling loops are two water pipes located underneath your boiler or near the water mains line that provides your boiler with water. These two taps control the flow of water into your boiler. If one of these taps is left open, it will make the boiler pressure too high.

The filling loop is a flexible pipe connected to two copper pipes with a tap at each end where they meet. Both taps should be closed.

A closed tap will be perpendicular to the water pipes. An open valve will be positioned horizontally. You can simply turn the taps to close them.

Once closed, monitor the unit’s pressure gauge to check for the return to normal boiler pressure.

Activate the pressure relief valve 

If your boiler pressure is too high, you can manually activate the pressure relief valve located on your unit. This can be quite dangerous as steam or hot water will be released when this valve is activated.

Let’s look at the steps you must go through to safely release boiler pressure.

  • Switch off your boiler and allow the system to cool down. Wait at least an hour.
  • Get a bucket and towel ready to catch any water released during the process.
  • Locate the valve by looking near your boiler or the pressure gauge. You can also check your boiler manual which will indicate the location and design of the valve for easier identification. Most pressure relief valves are activated with a lever or tap.  
  • Slowly start to open the tap or activate the lever of the pressure release valve and stand back in case any remaining steam or hot water is discharged.
  • Check the reading on the boiler pressure gauge and make sure the pressure drops to safe levels in the green zone.
  • Close the pressure relief valve back up. Make sure there are no leaks after closing the valve.
  • Switch your boiler back on and monitor its pressure for the next few hours.

Get professional help

You should call a professional if you still see the boiler pressure rising after following these steps. A qualified heating or Gas Safe registered engineer will be able to inspect the interior of your boiler and identify the root cause of your pressure issues.

Is High Boiler Pressure Dangerous?

Generally speaking, boiler pressure that is too high is not dangerous. All boilers are fitted with a pressure relief valve. This valve activates automatically whenever the pressure inside your boiler unit becomes dangerous.

We have all heard of cases of people’s boilers exploding. These stories only involve old conventional boilers with faulty pressure relief valves as well as a range of other issues.

However, a boiler under high pressure can cause water leaks and other damage around your home. It will also cause damage to your boiler’s internal components if not addressed.

How To Prevent High Boiler Pressure

The best way to prevent high pressure problems is to identify the causes early. Below we will discuss what you can do.

Check the boiler pressure gauge regularly

All boilers have a pressure gauge on display that you can keep an eye on to make sure your boiler is happy. You can check that the gauge’s needle is always within the green safe zone.

Whenever you spot the pressure getting too high, you can apply our simple steps to troubleshoot and treat the cause of the high pressure.

Perform maintenance once a year

We have discussed many causes of high pressure in your boiler. An annual boiler service from a heating or Gas Safe engineer would spot all those problems early.

An annual service costs between £60 and £120. It serves as an insurance policy against further boiler problems down the line. It will also extend the lifespan of your boiler.


Will the high pressure in my boiler drop on its own?

Yes, your boiler pressure increases and decreases as you use the unit. Whenever your boiler provides hot water, it will raise the pressure. When the boiler is not in use, the system will cool down and the pressure will drop.

However, this will not treat the root cause of the high-pressure problems you are facing. Follow our troubleshooting steps in this article and monitor the boiler. If the problem persists, contact a boiler technician.

Why is my boiler pressure too high and then too low?

A faulty expansion vessel will cause your boiler pressure to be too high during use. Then when the boiler cools down you will see your boiler lose pressure.

This is a problem that only a qualified heating engineer can fix. They will need to inspect your boiler interior or use a pump to re-pressurise the expansion vessel.


While high boiler pressure is not necessarily dangerous, it is a serious fault that you need to attend to. You can follow our steps to lower the boiler pressure while monitoring the system. If your boiler pressure increases again, it is time to seek professional help from a heating or Gas Safe engineer.

By using Eco Happy’s quote comparison service, you can get your high boiler pressure problems fixed by local technicians. Contact Eco Happy to find quality boilers at great prices.

James Elston

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

Leave a Reply

Your email address will not be published. Required fields are marked *