Boiler pressure too high – A fix-all guide.

boiler pressure too high or too low
inside combi boiler to check pressure

A high or low boiler pressure can be worrying to anyone who isn’t a gas engineer. First things first, it’s highly unlikely to be a risk to your safety.

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While it is true that both high and low boiler pressure can cause efficiency or maintenance problems, it’s very unlikely to cause any problems besides maintenance.

So, take a breath and then jump into our guide on what to do when your boiler pressure is too high or low. We’ll explore the basics, how to read your pressure, what pressure is best, and what could be causing problems.

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High Boiler Pressure – The Basics

Put simply, boiler pressure is the balance of water and air inside the boiler system. This includes the pipes as well. High boiler pressure means that there is an imbalance and your boiler needs to release some pressure to ensure it is working properly and efficiently

Balanced boiler pressure is necessary if you want to heat the water that travels around your home effectively and efficiently.

boiler pressure

Low boiler pressure

if the boiler pressure is too low this will also cause issues like your boiler to shut down or not passing hot water around your central heating system. be possible and can cause several other problems.

In fact, boiler pressure that’s too low or high is one of the most common reasons people replace and upgrade to a new boiler. But it’s not always necessary. First, take a look at the questions that are relevant to your situation below.

Is high boiler pressure dangerous?

Potentially as it can lead to water leaks around your home and electrics. High pressure on your boiler can cause efficiency problems which will cost you money on your gas bill. A pressure relief valve should kick in if boiler pressure goes high, but if this valve does not kick in, it can become dangerous. High boiler pressure can also cause other boiler problems like parts in your boiler to break such as the heat exchanger or any fixings.

boiler pressure gauge

Boiler pressure too high doesn’t sound good, does it?

You might have seen cartoons or other slightly less realistic TV programs where too much pressure results in the boiler exploding, but it can’t be that serious, can it? Yes, that is exaggerated, but too much pressure in your boiler is not good and if bleeding your radiators doesn’t work, then you must call a Gas Safe registered engineer.

Is low boiler pressure dangerous?

Good news, boiler pressure too low is not dangerous, but it can be likely to cause boiler problems, and it can affect the boiler efficiency and be costing you more money, or, in a worse case scenario a full new boiler cost.

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If your boiler is not working then it could be a simple pressure issue rather than needing a full boiler replacement.

Whether you have a Worcester Bosch, Viessmann, Ideal, Baxi, Vokera, or Vaillant, the boiler pressure can go too high and they can all loose pressure with no alarming underlying issue.

Before we get into what happens if boiler pressure is too high or what happens if boiler pressure is too low and how to solve it, it is important everyone reading this knows exactly what pressure is in the boiler and why it is so important.

My Boiler Pressure Is Too High?

What happens if the pressure is too high on your boiler?

You might be thinking “is your boiler pressure too high – how am I supposed to know?”. Boiler pressure should be between 1 bar and 2 bar. This is usually around 10 o’clock on most boiler pressure gauges.

If that was your first thought reading the title don’t worry because reading the pressure is quite easy.

That’s what the boiler pressure gauge is for after all.

This gauge will often have numbers and colours so you can tell at a glance whether the pressure on the boiler is too high or low. It should be around the 1.5 bar mark. More modern boilers have a green part that shows where your pressure gauge needle should be.

What’s the ideal boiler pressure?

The green 1 – 1.5 bar is the safe spot where you want to be.

boiler pressure
  • If you are hitting over 2.5, then you have too much pressure in your boiler.
  • If you are below 1 you have low boiler pressure.

While gauges will go higher in most cases, a boiler will shut off or breakdown if the boiler pressure is rising to 3 bar or 4.

However, if for some reason it hasn’t, and it doesn’t lower after a while, then you should shut the boiler off for your own safety.

If you do see the boiler pressure is too high when you have heating on don’t worry straight away.

If your boiler is busy heating up and someone is cleaning the dishes, someone’s taking a hot bath, and you have your radiators on then the pressure will naturally be higher. Sometimes it might even hit the 3 – 4 zone on the pressure gauge.

Don’t worry, though because this just means the boiler is currently experiencing a high water demand.

Once people turn off the hot water and radiators cool down the gauge will return to the more comfortable levels.

However, if you are constantly seeing boiler pressure rising to 3 bar which is classed as high-readings and you aren’t placing a higher demand on your water, then what could the problem be?

Well let’s go back to the first question I asked “Is your boiler pressure too high?”

If your boiler pressure is too high and there is no way it could be because of normal usage then it will likely be because of a fault.

Let’s look at some of the common causes in more detail.  

How to release pressure from a boiler

Releasing pressure from your boiler can be done simply by bleeding your radiators. If you have ever bled your radiators before then you will know you usually ahve to top up your water pressure on the boiler afterward at some point. This is basically the same. This may solve your problem, but if your pressure becomes high again quickly, you will need a heating engineer to check your system.

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Why is my boiler pressure too high? 

If your boiler pressure is too high then there could be multiple different causes.

Sometimes these boiler problems will be easy to fix, and you can even do it yourself without a Gas Safe heating engineer.

It could also be a much more complicated issue so let’s look at some of the common causes for boiler pressure problems.  

1. Boiler Age

If your boiler is over 10 years old and you are experiencing pressure problems, then there is likely a connection.

Boilers do naturally experience wear and tear and performance issues as they get older (don’t laugh) and will usually suffer from pressure problems.

So, in these cases, upgrading to a new boiler is recommended. Repairs might patch the problem for a while, but they aren’t going to be a long-term solution. Eventually, it could end up costing you more money.

If you need a new boiler, take a look at our guide to the best combi boilers, best system boilers or regular boilers.

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We have great boiler deals, offer finance on a range of boilers, all from £9.50 to £17 per month on a replacement boiler.

If you have a back boiler, then we will struggle to help you, but you may find out back boiler replacement guide helpful.

2. Faults and Malfunctions 

There are numerous components in a boiler-related to measuring/ dealing with the pressure. If these get damaged in some way or malfunction, then your boiler’s pressure could easily rise or have no boiler pressure.

The pressure release valve and filling loop are the two most common culprits for the boiler pressure.

You can inspect these yourself but in the majority of cases calling in a professional Gas Safe heating engineer is advised unless you really know what you are doing.

gas safe installer

The good news is if the issue it quick and simple, it might not cost much to fix although if you need replacement parts, it will be more expensive.

Always remember you may have a warranty to cover the issue. Whether your Worcester Bosch boiler pressure gauge is not working, Vaillant boiler pressure is too low, Baxi combi boiler pressure is too high, it is always worth checking the warranty.

3. Too Much Water

boiler leaking water

Can a boiler have too much water?

Is your boiler leaking water?

That might sound like a riddle, but the answer is yes, your boiler can have too much water. If it does, it can cause problems, especially where pressure is concerned.

But going from too little water to too much water is still a problem, isn’t it?

To diagnose this problem, you simply shut the boiler off and see what the pressure gauge says. If the boiler pressure gauge reads 1.5 or more, then you likely have too much water in the system.

But how do you release too much water from the system?

Thankfully realising boiler water pressure from the system is quite simple and in most cases simply bleeding your radiators will get rid of the excess water and return the normal boiler pressure.

It might sound painful but all you have to do is turn the safety valve a little on your radiators and let some excess water drip out.

Monitor the gauge while doing this and stop when it reaches back into the safe green zone.

Error Codes for High Boiler Pressure

ideal boiler error code

Before you go and inspect your boiler pressure gauge because this blog has probably made you a little anxious.

You should know that many modern boilers will also run error codes on their control panels. Error codes run if they are detecting problems with the boiler pressure.

Keep your boiler instruction manual handy or be prepared to search online for it. If both of the above fails, you can call the manufacturer if you spot some error codes and think they relate to your boiler’s pressure.

Error codes are a great way of catching a problem early that might not show up on the pressure gauge right away.

Your boiler pressure may be high but this could be a simple fix rather than a new boiler installation

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Q What kind of fuel does your boiler use?

We have great boiler deals, offer finance on a range of boilers, all from £9.50 to £17 per month on a replacement boiler.

If you have a back boiler, then we will struggle to help you, but you may find out back boiler replacement guide helpful.

How risky is high boiler pressure?

boiler overflow pipe leaking

Exploding boilers like I said earlier are pretty much the work of cartoons and dramatic movies.

High pressure doesn’t equal instant explosion.

In fact, most boilers that have too high pressure will shut down due to the pressure release valve or just break down because they can’t handle the stress (yeah we can all relate to that can’t we).

They will likely spring leaks and might soak your carpet or kitchen, but usually, there will not be a huge explosion.

What to do if your boiler pressure is too high and can’t be fixed?

boiler cover (service)

If your boiler is on the blink and you think that you need it fixing, contact a Gas Safe heating engineer or firstly check your manufacturer’s warranty to see if you are covered.

Alternatively, you may need a new boiler.

We can offer boilers on finance or cash outright with a fixed online boiler quote within minutes.

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We can, however, help you if you require a combi swap or a system boiler conversion. 

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