What to do when your boiler pressure is too high

What pressure should my boiler be?

Your boiler’s pressure is usually displayed on the built-in pressure gauge. It should read around the 1 bar mark when you’re not running any hot water and the heating isn’t turned on. 

When the heating is turned on, your boiler pressure should be between 1.5 and 2 bars. Most boilers will highlight this area in green on the pressure gauge, clearly showing you that the pressure setting is correct.

If the boiler reading is outside these numbers, this indicates that the boiler pressure is either too low or too high.

Boiler pressure at a glance 

When the heating is turned on, here’s what you need to know about your boiler pressure:

Symptoms of high boiler pressure

Aside from the pressure gauge, there are several symptoms that can indicate your boiler pressure is too high, such as:

• Noises from your boiler: Gurgling, banging, or whistling sounds can be a sign of excess pressure causing stress in the system. These noises from your boiler often indicate something isn’t working as it should.
• Boiler shutdown: When the pressure gets too high, some modern boilers are designed to shut down automatically as a safety precaution. In the event of high the pressure release valve (a small pipe leading from the boiler to outside your home) will open, relieving the pressure in the system. This prevents damage to internal components and helps avoid potential hazards.
• Leaking: Excessive pressure can cause seals to fail or force water out through the pressure relief valve or weak points in the system, leading to visible leaks around the boiler or pipework.

Why is my boiler pressure too high?

If your boiler pressure is too high, some common reasons behind it include:

• Overfilled system: If too much water has been added when topping up the boiler, it can push the pressure above safe levels.
• Faulty valves: Filling loops that are stuck or damaged may allow water to enter the system continuously or fail to release excess pressure.
• Faulty expansion vessel: This vessel absorbs the pressure increase when water heats up. If it's damaged or loses its air charge, it can't do its job properly, causing pressure to rise.
• Leaks: Oddly enough, a leak can sometimes lead to overcompensation in water refilling, resulting in high pressure.
• Faulty pressure gauge: If the gauge itself is malfunctioning, it may give a false reading, making the pressure seem higher than it really is.

How to reduce your boiler pressure in three different ways

Reducing boiler pressure can be as easy as bleeding your radiators and letting a little water out of your heating system. One of our Home Experts, Chris, explains how to reduce high boiler pressure safely in the video below. Or you can follow the full step-by-step guide.

Method 1: Bleed your radiators

1. Before bleeding your radiators, you’ll need to switch off your boiler and wait for the heating system to cool.
2. Ensure the filling loop or relief valve is tightly closed to prevent further water from entering the system, which could increase pressure.
3. Find the small valve at the top of the radiator, usually on one side.
4. Place a cloth or container underneath and hold a cloth or small bowl under the valve to catch any drips of water.
5. Insert the radiator key. Fit the key onto the valve and slowly turn it anti-clockwise. You may a hissing sound as trapped air escapes.
6. Keep the valve open until water comes out. If you can, keep an eye on your boiler’s pressure indicator so you know when to close the valve.
7. Turn the key clockwise to close the valve securely.
8. Check to see if the boiler pressure returns to its correct setting.

Method 2: Use a drain-off or filter valve

1. Turn off the boiler. Make sure the system is switched off and has cooled down.
2. Locate the drain-off or filter valve, often near a pipe or filter.
3. Place a bucket underneath to catch the water.
4. Turn the valve anti-clockwise slowly to release water from the system. Do this gradually to control how much pressure you're letting out.
5. Keep an eye on the boiler’s pressure gauge and stop draining once it reaches the recommended level (around 1 to 1.5 bars when cold).
6. Once the pressure is correct, turn the valve clockwise to close it securely.

Method 3: Professional assessment

If you’ve tried the fixes above and your boiler pressure is still too high, or the issue keeps coming back, it might be time to get a professional assessment. Sometimes, the problem isn’t something you can easily spot or sort on your own.

For example, if the pressure relief valve is faulty, it may need to be replaced by a qualified engineer. Similarly, a faulty expansion vessel can cause pressure fluctuations and might need to be recharged or replaced.

In cases like these, getting a Gas Safe Registered engineer to take a proper look at your system will identify any underlying issues and recommend the best solution. It’s a great way to get peace of mind and make sure your boiler is running safely and efficiently. Plus, it can help you avoid bigger (and more expensive!) problems down the line.

Important considerations when your boiler pressure is too high

When dealing with high boiler pressure, safety should always come first. If you’re not qualified, it’s important not to attempt any repairs or adjustments that aren’t safe to do without a professional.

To help prevent issues like high pressure from developing in the first place, regular boiler servicing and maintenance can go a long way in preventing issues like high pressure from developing in the first place.

Alongside this, it’s also a good habit to keep an eye on your boiler’s pressure gauge. Checking the readings regularly can help you spot any changes early and take action before it becomes a bigger problem.

Boiler pressure still too high?

If you’ve tried everything and your boiler pressure is still too high, there could be one of the following issues:

• The expansion vessel is faulty and may either need repressurising or replacing
• There’s a fault with the filling loop
• A pressure gauge malfunction

Is high boiler pressure dangerous?

In most cases, high boiler pressure is not dangerous if the boiler has a working PRV (pressure relief valve). When the pressure becomes too high, the boiler will either turn itself off, or the PRV will release excess pressure by dumping it into a drain or safe location.

That being said, high pressure can lead to other problems, such as leaks that can cause damage to your heating system and boiler. So you shouldn’t rely on the PRV. As soon as you notice your boiler’s pressure is too high, make sure to follow the steps in this guide to fix it as soon as possible.

If the problem keeps coming back or you're unable to fix it yourself, it could point to a deeper issue within the system. In that case, it’s best to call in the experts—one of our Gas Safe Registered engineers will be happy to take a look and get everything running smoothly again.

Is your boiler pressure too low?

If your boiler pressure is too low (anything below one bar), you may need to top up the water in the boiler using a filling loop. Alternatively, there may be a leak in your heating system.

Low boiler pressure may result in no heating or hot water, meaning that your central heating system will have to work harder and ultimately use a higher amount of energy.

Boiler repairs you can count on

If you haven’t been able to fix your boiler pressure yourself, it’s a sign that a professional needs to step in.

That’s where Ding can help. With a home repairs membership, you’ll get access to our trusted, Gas Safe Registered engineers who can sort things out quickly and safely. No chasing around for quotes or waiting weeks for help, just clear pricing, fast availability, and expert service when you need it.

Try Ding today and let us take the stress out of home repairs.