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Last Updated on October 16, 2023

Why is my boiler pressure too high?

Is your boiler pressure too high? While there are a number reasons for this happening, if you respond quickly and appropriately, it can be a thing of the past.

In this article you’ll find all the answers you need to questions like ‘What is boiler pressure?’, ‘Why is my boiler pressure too high?’ and ‘How to lower boiler water pressure’ that can help you understand the issue and ultimately get rid of it.

Having a boiler break down and constantly give you a hard time with the pressure can understandably cause a bit of an upset. However, if you’ve done the research into boiler breakdowns, or if you’re simply researching why your boiler stopped working in cold weather, you can relax – you’re already on the right track.

By choosing a premium, high quality installer with a strong relationship with their manufacturer, they can provide more thorough, experience-based advice to help you choose a boiler that’s right for you.

Alternatively, if you’d like to get a free, no-obligation quote from us directly, you can do so by entering your postcode below, then hitting the button! Easy!

Lets sort out that high boiler pressure!

High boiler pressure may be caused by several factors, including:

  • Overfilling of your heating system
  • Faulty boiler components such as an expansion vessel and Filling Loop
  • External filling loop is functional, but still attached and letting-by water

As well as this, you may find that you’re dealing with ‘boiler pressure too high’ a bit too often because of your boiler’s age. If it’s too old, components such as the heat exchanger can degrade in quality which causes issues like this to surface.

Thankfully, there’s always a way around this. By speaking to one of our in-house experts at Boilerhut, you can get all the information needed on how to move forward. Alternatively, if you’re interested in an entire boiler replacement, you can enter your postcode in the box below, then hit the green button for a FREE, no-obligation quote.

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 What is boiler pressure?

In a few words, boiler pressure refers to the balance in air and water that occurs from inside your boiler. It’s what pushes your hot water through your property’s heating system. Therefore, if your boiler pressure is too high, it’s going to cause some issues. If it’s too low, then you’re going to struggle getting things heated properly.

The pressure on your boiler may change for several reasons, but if it’s too high, the sooner you deal with it, the better.

What pressure should my boiler be?

When asking ‘what should my boiler pressure be?’, it’s important to recognise that not every boiler has the exact same requirements for water pressure.

The general rule however, is that most central heating systems within the UK will need their pressure set between 1 and 2 bar – around 1.4 is ideal. This will equate to between 14 and 29 PSI (pounds per square inch).

How do I find out my boiler’s pressure level?

The only way to keep track if you’re asking ‘What pressure should my boiler be?’, is by looking at the pressure gauge yourself. In most cases, it’ll be located at the very front of the boiler, usually displayed on the front panel.

where is the pressure gauge on my boiler

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Why is my boiler pressure too high?

Before going any further, you’ll need to determine whether or not your boiler’s pressure is still rising, or if it’s been set too high and you need to bring it back down.

Overfilled system

An overfilled system is the most likely cause of boiler pressure too high for most people.

When we repressurise, we use the filling loop directly below the boiler to add more water and as a result, increase the pressure. If you’ve recently had to repressurise the boiler, you may have come across this issue.

To put it simply, your boiler needs the right amount of water in order to operate properly. When we use the filling loop however, the system can sometimes be overfilled and when it does, your boiler is put under a lot of strain. Continuing with this damage may result in:

  • Pipe joints being more likely to fail (if it’s an older system)
  • Cracks forming on heat exchanger and other important components

How to fix an overfilled heating system

Thankfully, solving this problem can be relatively easy, since all you’re essentially doing is draining some of the water from the system. You can either use the bleed valve from any one of your radiators or the drain cock to carry this out.

If you’re already aware of where the drain cock is in your property, you can drain the system and then use a small hose before opening the valve a little bit. Doing so will allow water to escape, but you may need somebody with you if you’re using this method. This is not only to make sure the water escapes safely, but to keep an eye on the pressure as well.

Not sure where the drain cock is? Not to worry – you can also drain your system by bleeding one of your radiators.

How to bleed a radiator

For detailed instructions on how you can bleed a radiator, please watch the short video (here >). Or alternatively, you can click here to read our 6 easy steps to bleeding a radiator.

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Faulty boiler components

The quality of your heating largely depends of the quality and condition of the boiler itself. There are several components found within your boiler that could be a reason for your boiler pressure too high, so you’ll need to check them to see if you have to deal with any other problems. These include:

  • Filling Loop
  • Expansion Vessel
  • PRV (Pressure Relief Valve)

What is a Filling Loop?

A boiler filling loop provides a temporary connection to the mains, allowing you to repressurise and fill your heated system with water. Depending on the make of the boiler, these can either be external and detachable, or internal. In almost all cases, they have a braided-hose design and sit right below your boiler. You may also notice one or two black taps by this filling loop – double check that these have been closed by making sure they’re perpendicular (90 degree angle) to the pipe.

A filling loop that has been left slightly open is one of the more common causes of boiler pressure too high. If you have an external filling loop, always make sure the taps are completely closed.

Your boiler filling loop plays an important role in raising your boiler’s pressure if it’s too low. For instructions on how this can be done, take a look at the video (here >).

What is a PRV (Pressure Relief Valve)?

The PRV is what is used to prevent a buildup of pressure inside your boiler. Self-explanatory in function, it’s designed to open and release pressure if it gets too high. Once it drops to a safe level, the valve closes again. These are used for a wide range of functions beyond central heating, including clean water and petrochemical/power generation industries.

Below is a cross section of a typical pressure relief valve. If you look towards the far end, you’ll notice a light blue screw. During operation, this screw gets lifted by the (dark blue) spring underneath, allowing the pressure to escape. As this same spring is moving up and down, the light blue screw on the end does so as well to keep the pressure inside.

Pressure Relief Valve Cross Section

Is it dangerous to have high boiler pressure?

In most cases, it’s not too much of a problem. Having a Pressure Relief Valve means your boiler is ready once the pressure gets too high. However, the situation can still worsen to the point that you may need to replace your boiler entirely. This is obviously a last resort, but be aware that if you don’t take care of your boiler, things like this can still happen. Just like human beings, boilers on ‘high pressure’ can struggle to stay operational if they’re not properly cared for. If untouched, an overpressurised boiler can develop cracks which then causes leaks. To stop this from occuring, always make sure to:

  • Check the pressure levels of your boiler regularly
  • Contact a professional who can give you appropriate advice and support
  • Be aware of how to bleed your radiator if your pressure is slightly too high
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What to do next?

As you’re probably aware with most problems in life, the quicker they are dealt with, the quicker they can be solved and you can continue with your day-to-day life. So if you’re finding that ‘boiler pressure too high’ is an issue that’s been coming up frequently, it’s worth considering that you might actually be better off with an entire boiler replacement.

It’s important that you don’t do anything you’re not qualified for in this situation. Having a professional assess the issue not only means you can get that much-needed reassurance, but that your warranty remains unaffected. Any tampering with the product is likely to affect your warranty, meaning you’ll be even more stuck finding a solution to the problem.

Get advice for a new boiler

Most boilers should last you up to 15 years before you need a replacement. However, if you know you’ve already reached that point, the next thing you need to do is speak directly with a heating expert for some genuine advice and support. It’s also worth speaking to an installer who has good relations with their manufacturers. In the case of Boilerhut, we are Premium Viessmann Installer, and can provide you with reliable, experienced advice to help you decide which boiler is best for you.

If you’d like to find out more about how Boilerhut can help, you can either:

  • Send us an email with any queries straight through to
  • Call us directly on 029 2009 9898 to speak to one of our in-house advisors
  • For a FREE, no-obligation quote, enter your postcode in the box below and the hit the green button
Get Your FREE Online Quote Today!
Save up to £590 PER YEAR on your heating bills.
Getting a quote takes less than 2 minutes. No obligation.
Save up to £590 PER YEAR!
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