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Last updated: 8th April, 2024


Boiler Pressure Too High

Boiler Pressure Too High

Key takeaways

  • Overfilling: Adding too much water can increase boiler pressure beyond safe levels.
  • Faulty Pressure Relief Valve: A malfunctioning valve can cause excessive pressure build-up.
  • Thermal Expansion: Heat expansion in the system can lead to increased pressure if not regulated properly.

What happens when your boiler pressure goes too high, some possible causes and how to fix it.

The pressure gauge on your boiler needs to be just right for it to run efficiently and safely. If you notice that boiler pressure is too high, this can be dangerous and will cause issues within your hot water and central heating system.

This guide is here to explain why your boiler pressure is too high and how this can be resolved, we also have a quick video available below which can help with boiler pressure issues.

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What Is Boiler Pressure And Why Is It Important?

'Boiler pressure' refers to the water pressure within the boiler. The balance of water and air, within the machine, determines the boiler's pressure and these needs to be kept at a reasonable level to ensure that the boiler is gas safe, which is extremely important for your safety, and working well.

The boiler's pressure takes place in the pipes and components of the system, and it can be dangerous if there is too much pressure building up within the system.

There are also issues to deal with if the pressure is too low, our guide on what to do if this is the case can be found here.

Whether you need to reduce your boiler pressure or bring it back to a standard, it is a good idea to consult an engineer. In some cases, a boiler replacement might be a better option, than actually dealing with the issues caused by high or low pressure as a new model can be bought for a fixed price rather than the various expenses of getting your boiler fixed.

How to Read Boiler Pressure

The ideal boiler would be able to tell you when the pressure may need adjusting and then call an engineer for you, but unfortunately, that is not the case.

Instead, you have to keep an eye on the boiler pressure gauge to see whether your combi boiler is working as it should.

On most boilers, it is easy to see when the boiler pressure enters a dangerous zone because of the colours and numbers on the gauge.

Your boiler should be running between the 1 bar and the 1.5 bar, which will be in the green section of the boiler pressure gauge.

If the bar is hitting over 2.5 bars, then the pressure from the water in the system is too high, and anything below 1 bar is too low.

Once the boiler pressure is too high or low, your heating system should automatically shut off to keep it safe. A new boiler model like the Worcester BOSCH 8000 will shut off automatically at a high pressure of three or four bars.

Sometimes high pressure is not always an issue in your boiler, as it can just indicate high demand for water from the system. You will see the release valve go down if this is the case once you have stopped running water in the home, such as from washing dishes or running a bath.

However, if your boiler pressure is too high, at around the 3 bar, without additional demand for hot water, then there is an issue.

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Common Causes of High Boiler Pressure

If the boiler pressure is consistently too high, then there is likely an issue with your system.

Let us take a look at some of the common causes of high boiler pressure:

Boiler Needs Replacing

You should only use a boiler for 10 years before it needs to be replaced. There will come a time when your boiler can no longer be fixed as the problems will either be too expensive or too difficult to solve.

If this is the case, then you might be better off buying a new boiler rather than trying to get your old system fixed.

It is possible to get financial support when you need to replace your boiler, however, make sure to go through a credit broker that is authorised and regulated by the Financial Conduct Authority in England.

Standard Faults

The expansion vessel, pressure release valve and the filling loop are some of the common causes of too much water or air pressure in your boiler.

You could check these kinds of valves yourself, but usually, boilers need to be assessed by a gas safe engineer to ensure that your home has safe access to heating and hot water.

In most cases, boilers that have a faulty valve of this kind can be easily fixed, and it does not have to cost a lot to do so.

Make sure to call an engineer as soon as you notice problems with your boiler to get the right solution and keep your home safe.

How to Fix High Pressure Boilers

You might find that you can solve the issues with water pressure yourself if they are not too complicated.

If the issue lies in one of the valve controls we have mentioned, you may find it easy to solve yourself. For example, a filling loop may have to be re-pressurised to solve your issues.

There are other causes of boiler pressure too. Having too much water in boilers is one of the problems you may be able to fix on your own.

To reduce boiler pressure caused by too much water, you first need to check that this is the problem. You can do this by switching the boiler off and seeing what the pressure gauge says.

If the pressure is higher than 1.5 bars, then the pressure is too high.

It is easy to pressure release water from a boiler and fix this issue. In most cases, all you will need to do is bleed the radiators in your home using a radiator key to release some of the pressure.

There is a pressure release valve on every radiator that you can easily find. Turning this will help release pressure from the boiler.

You should only open the radiator valves a little bit and let them bleed until the excess water has come out of your boiler, which you can track using the pressure gauge.

For this, you should get towels or other floor coverings to keep surfaces dry when bleeding radiators around the house.

Call for Help

If your boiler is more than 10 years old, then it is time to get a new central heating system installed in your home. This could be cheaper than the cost of fixing your old one, as most boilers come at a fixed price that you can budget for.

While engineers commonly do not work for a fixed price, use their services if you are having issues with heating your home. This could make things easier for you and get the problem sorted faster than you doing it yourself.

Having a broken boiler is never ideal, but with engineers on your side, you can get the heating working again in no time! Give us a call today on 0333 305 6880, or use our online quote engine to receive a fixed price quote for a new boiler.

Ideal Boilers Exhibiting High Pressure Symptoms

Error Code for Pressure Issues F1

This code is typically accompanied by written messages indicating pressure problems. The F1 error code in Ideal boilers primarily signals high pressure, which could be symptomatic of other underlying issues.

Models That Might Be Impacted

This issue commonly arises in models such as Logic, Logic Plus, Vogue, Vogue Max, Mini, and Isar. Each of these models has unique features, but they may share similar vulnerabilities to pressure-related problems due to design similarities.

Usual Causes

High pressure indicated by the F1 code could be due to several factors:

System Overfill

This happens when the water level in the boiler exceeds the recommended limit, potentially due to user error or malfunctioning automatic filling systems.


Faulty components or connections can lead to leaks, inadvertently increasing system pressure.

Recommended Approach: Step-by-Step Troubleshooting

Safety First: Ensure the boiler is switched off and cooled down before attempting any checks.

Check Water Level: Consult your boiler's manual to find the optimal water level and adjust if necessary.

Bleed Radiators: This can release any trapped air, which might be contributing to the high pressure. To bleed a radiator, use a radiator key to slowly turn the valve, allowing trapped air to escape until water starts dripping out.

Inspect for Leaks: Check for visible signs of water leakage around the boiler and pipe connections.

Preventive Measures

Regular Maintenance: Schedule annual check-ups with a certified technician to prevent common issues.

Monitor Water Pressure: Keep an eye on the boiler's pressure gauge, ensuring it stays within the recommended range.

When to Call a Professional

Persistent display of the F1 code or inability to rectify the issue through these steps necessitates intervention by a Gas Safe registered engineer. They possess the necessary skills and certification to safely and effectively resolve boiler issues.

Elevated Boiler Pressure in Worcester Bosch Models

Error Codes Indicating High Pressure

The E9, A1, 224V, 1065B, and 2970B error codes are common indicators of high pressure in Worcester Bosch boilers. These codes help in diagnosing the specific nature of the pressure issue.

Affected Models Include

Greenstar series (25i, 30i): Known for their efficiency, these models may encounter pressure issues due to their compact design.

CDi range (Standard, Classic, Compact, Highflow): This range, while versatile, can be prone to pressure irregularities, especially in systems with fluctuating water supply.

Potential Reasons

Overfilling: Excessive water in the system can lead to increased pressure.

Malfunctioning Expansion Vessels: A faulty expansion vessel may fail to absorb excess pressure.

Component Issues: Valves, seals, or pumps might be contributing to pressure problems.

Suggested Measures

Check Water Level: Ensure the pressure gauge reads within the manufacturer's recommended range.

Bleed Radiators: This process involves opening the bleed valve to release trapped air.

Professional Consultation: Codes like E9 should be investigated by a Gas Safe engineer due to their complexity.

Preventative Tips

Regular maintenance checks and monitoring the system's pressure can help avoid these issues.

High Pressure Issues in Vaillant Boilers

Error Codes Commonly Seen

F.12, F.74, F.75, S.41 are indicative of high pressure. Each code may point towards specific pressure-related problems.

Models Often Affected

EcoTEC series (Standard, Pro, Plus): These models, while highly efficient, can show susceptibility to pressure changes.

EcoMax and ecoFIT: Known for their advanced features, they require careful monitoring to maintain optimal pressure levels.

Typical Causes

Expansion Vessel Issues: Faulty expansion vessels often lead to pressure imbalances.

Excessively High Water Pressure: This can occur due to overflowing or a malfunctioning pressure release system.

Action Steps

Cool Down Procedure

Before any checks, ensure the boiler is off and cooled down.

Pressure Assessment: Reassess the pressure after the boiler has been off for a while.

Gas Safe Engineer Consultation: If codes like F.75 persist, it’s crucial to seek professional assistance.

Long-Term Care

Maintaining regular service appointments and being vigilant about pressure readings are key preventive steps.

In each section, detailed steps, potential causes, model-specific information, and preventive measures are included to guide readers more effectively. Safety and the need for professional intervention are also emphasised, particularly for complex issues indicated by specific error codes.

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Frequently Asked Questions

How do I get the pressure down on my boiler?

To reduce the pressure in your boiler, you can try bleeding the radiators, which involves releasing trapped air that can cause an increase in pressure. Ensure that your boiler is switched off before attempting this. If bleeding the radiators doesn't help, you may need to drain some water from the system using the drain valve. If the pressure remains high, consult a professional engineer for further assistance.

Why is my boiler pressure rising to 3 bar when heating?

Boiler pressure can rise due to trapped air in the system, a faulty expansion vessel, or a malfunctioning pressure relief valve. If the pressure rises to 3 bar, it's an indication that there may be an issue that requires professional attention. Reach out to a heating engineer to diagnose and fix the problem.

Is it dangerous to have high boiler pressure?

Yes, high boiler pressure can be dangerous as it increases the risk of leaks, which could lead to water damage or even a complete boiler breakdown. Moreover, if the pressure is too high, the boiler might stop working as a safety measure. Keeping the boiler pressure within the recommended levels is always best to ensure safe operation.

What should the boiler pressure be when the heating is off?

The boiler pressure should be between 1 and 1.5 bar when the heating is off. This range is generally marked in green on the pressure gauge. When the heating is on, the pressure could be slightly higher, between 1.5 and 2 bars.

How can I fix a boiler pressure that is too high and leaking?

If your boiler pressure is too high and leaking, try to release the excess pressure by bleeding the radiators or draining some water through the drain valve. If the issue persists, there may be a problem with the pressure relief valve or expansion vessel. In this case, it's essential to contact a professional heating engineer to diagnose and repair the issue.

How can I lower the boiler pressure without bleeding radiators?

One way to lower the boiler pressure without bleeding radiators is to drain some water from the system using the drain valve. Be cautious while doing this, as the water might be hot. You should also ensure your boiler is off before attempting this procedure. It's always best to consult a professional heating engineer if you're unsure.

Why is the pressure on my combi boiler too high?

Pressure on a combi boiler might be too high for several reasons, including trapped air in the system, excessive amounts of water, a faulty expansion vessel, or a malfunctioning pressure relief valve. If you notice your pressure is consistently in the red zone (above 2 bars), you must contact a heating engineer to diagnose and fix any underlying issues.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.