What Pressure Should a Combi Boiler Have?

If you’re the type of person who glances at your boiler once a year or only when it starts acting up, this guide is for you. 

Don’t sweat it if you don’t know what pressure your boiler should be at, because that’s exactly what we’re going to explain here. 

Heating Savvy teaches you in this guide what pressure a combi boiler should have.

What Exactly is Boiler Pressure?

Boiler pressure refers to the pressure of the water in your heating system and boiler.

You can monitor your boiler pressure using the pressure gauge. A small gauge or dial usually located on the boiler’s front.

This gauge will display the system’s pressure to help identify any leaks or pressure drops.

Checking your boiler pressure can help you detect any issues with the boiler.

Such as whether your boiler pressure is too high and risks causing a system overload. Or too low, which may lead to problems with the system and the boiler.

Why is Boiler Pressure Significant?

Your boiler’s pressure determines the effectiveness and efficiency of your entire central heating system.

Maintaining the correct pressure level is crucial for generating heat throughout your home.

But what happens when your boiler pressure is too high or too low? I’ll show you right away.

What’s the Ideal Pressure for Combi Boilers?

Your combi boiler’s pressure should ideally be between 1 and 1.5 bar.

If your pressure gauge reads less than 1 bar, it’s possible that water has escaped from the system due to a leak.

If it reads at 2.8 bar or higher, you might need to bleed a radiator to decrease the pressure to an appropriate level.

When doing this, ensure you have a means of collecting the water to prevent damage to your walls or flooring.

Be careful as the water can be extremely hot. If you’re uncertain about any step, it’s advisable to call a professional engineer.

If you discover a leak or suspect one, you should call a plumber who can diagnose and rectify the issue.

If you believe the pressure has gradually decreased over time, you can adjust the boiler pressure yourself.

What is the normal pressure for a boiler?

The pressure on the boiler gauge should be between 1.0 and 2.0 bar.

If the pressure drops too low, the boiler goes into fault mode and displays an error code. For example:

• Vaillant boiler error F22 – Too little water in the boiler;
• Viessmann boiler error F2 – Lack of water;

You need to charge the system with water as described above, through the filling loop.

If the boiler pressure exceeds 3.0 bar, the boiler’s safety valve will open, and water will flow from the boiler.

How do you know if your boiler pressure is good

The million-dollar question is: how do you know if your boiler pressure is good? 

Well, your boiler’s manual is your trusty friend in this case. 

It contains detailed instructions on how to recharge your heating system if your boiler pressure isn’t normal. 

Boilers have a control pressure gauge on the front panel that looks of the boiler.

For floor boilers with a burner, pressure gauges are mounted separately on the supply and return pipes.

For open circuit heating systems (with an open expansion vessel), no pressure gauge is mounted because these are not pressurized.

How Regularly Should I Check My Boiler Pressure? 

It’s advisable to routinely monitor your boiler’s pressure gauge. Ideally every few weeks, to ensure it’s not excessively high or low. 

This habit will help ensure you detect any signs of a problem early, and they are addressed as soon as possible.

Often, if left unattended, problems can worsen and end up costing more to repair. 

If you have just vented your radiators, it’s also a good idea to check your boiler pressure hasn’t dropped too low. As you may need to top it up. 

How Frequently Should You Re-pressurise a Combi Boiler?

There’s no specific timeline for when you should re-pressurise your combi boiler.

You should do it when the pressure has fallen to below 1 bar.

This indicates that water has been lost from the system and needs to be replenished.

You shouldn’t need to do this often. If you find yourself doing it more frequently than expected, contact your installer as your boiler might be leaking.

Why do I need to charge with pressure?

The water in the heating system needs to be at a certain pressure for the boiler to function properly.

There’s a pressure sensor in the boiler, and if the pressure drops below 0.8 bar, the boiler goes into fault mode.

This happens to prevent it from operating without water and risking overheating.

How do you increase the water pressure in your boiler? 

If the water pressure is below 1.0 bar or below 0.8 bar, you need to recharge the system with water until it returns to normal. 

This is a simple maintenance operation that you can easily do yourself, and it’s best done when the radiators are cold. 

Let me explain the steps to restore the pressure in your boiler.

How do you fill the heating system with water? 

The boiler’s filling tap is mounted at the bottom of the boiler or on one of the supply or return pipes.

While keeping an eye on the boiler’s gauge, slowly open the charging tap. When the gauge needle reaches between 1.0 and 2.0 bar (preferably 1.5 bar), close the filling tap. 

If you’ve overfilled with water, and the gauge needle is at 2 or 3 bar, you need to reduce the pressure. You can do this very easily.

Bleed one of the radiators and let the water flow from the radiator vent into a container.

This will cause the boiler pressure to drop until it returns to normal.

If the pressure exceeds 3 bar, the boiler’s safety valve will discharge, allowing water to flow to protect the heating circuit. 

Remember, keeping an eye on your boiler pressure is not just about ensuring your heating system works efficiently.

It’s also about ensuring the longevity of your boiler. So, don’t be a stranger to your boiler’s pressure gauge!

Internal Filling Loop Type

The Worcester Keyless Filling Link enables you to swiftly and effortlessly re-pressurise your heating system without the need for a separate filling loop or key.

The keyless filling link is easy to locate and simplifies the re-pressurisation of your heating system. Here’s how to do it:

• Locate the Small BLUE Lever beneath your Worcester combi boiler
• Pull the lever down and hold
• Monitor the pressure gauge & release the lever when the pressure gauge reaches 1.5 bar
• Switch the boiler back on and recheck the pressure gauge
• Depending on your boiler make/model you may need to reset your boiler – if you are unsure check your boiler manual
• Open a hot tap & check that your boiler fires & your water heats up

By re-pressurising your boiler, you’re allowing more water to enter the system from the mains supply.

If you accidentally over-pressurise the system, don’t panic. You may need to vent your radiators to bring the pressure back down to 1.5 bar.

You should monitor the pressure over the following days and weeks to ensure the pressure doesn’t drop again. If it does, there’s a chance you may have a leak.

How do I reset the boiler?

Some boilers go into fault mode if the pressure is too low. For example, a Vaillant boiler doesn’t operate below 0.8 bar.

If the boiler has gone into fault mode and you need to reset it, many boilers have a reset button that needs to be pressed.

Why does the boiler pressure drop?

Over time, it’s not unusual for the boiler pressure to drop slightly. 

But if the pressure drops regularly, it may indicate that you have a leak somewhere in the radiator circuit.

Is Low Boiler Pressure a Cause for Concern?

No, low boiler pressure isn’t dangerous.

Sometimes, heating systems have small leaks – similar to a slow puncture in a tyre.

While you might not notice any water escaping, over time the pressure in the system falls until it’s too low.

If you’ve just vented the radiators, you might also see the boiler pressure dropping.

Venting the radiators removes any air in the system, which can cause a change in the boiler pressure.

Is High Boiler Pressure a Cause for Concern?

No, it’s not typically dangerous. The heating system is protected by a boiler pressure relief valve (PRV).

This valve prevents damage by allowing water to escape, Sometimes via a small pipe through the external wall near the boiler, when the pressure is too high.

Most systems also shut down if boiler pressure gets too high.

How do I lower the boiler pressure if it’s too high?

If the boiler pressure gets close to 3 bar, the boiler’s safety valve will discharge, and you can see water flowing from the boiler. 

You can lower the boiler pressure when you vent the radiators or drain some water out of the circuit.

So, what pressure should a combi boiler have? 

The normal operating pressure for the heating system is between 1.0 and 2.0 bar.

To check the pressure, look at the gauge on your boiler’s panel. If the needle is between 1 and 2 bar, you’re golden.

But if the boiler pressure is too high or too low, you could run into problems.

How Frequently Should You Re-pressurise a Combi Boiler?

There’s no specific timeline for when you should re-pressurise your combi boiler.

You should do it when the pressure has fallen to below 1 bar.

This indicates that water has been lost from the system and needs to be replenished.

You shouldn’t need to do this often. If you find yourself doing it more frequently than expected, contact your installer as your boiler might be leaking.

How to Lower Boiler Pressure

Want to know how to decrease boiler pressure in your system by yourself?

You can attempt to identify the problem in a few simple steps – and lower the boiler pressure:

• Switch off the boiler.
• Ensure that the filling loop valves, or the key or keyless filler, are fully closed.
• Wait for the system to cool, then release pressure by venting each of the radiators. 

Be cautious as it’s easy to vent the radiators incorrectly. So if you’re unsure or encounter a problem while carrying out the vent – the pin gets stuck or you can’t get it back in the valve, for instance – call a professional immediately.

After venting every radiator, check the pressure gauge. If it’s still too high, you’ll need to repeat the process of venting one or more radiators.

Keep checking until the boiler pressure gauge reads around 1.2 bar – or at least has returned to the green zone.

If the boiler pressure ends up too low, follow the instructions above to top it up again. But be sure to close off the filler valves afterwards!

If your boiler pressure keeps rising into the red, it’s best to arrange a boiler repair.

It could indicate a problem with the pressure relief valve – or a fault within the system. 

How frequently should i need to adjust the pressure in the heating system?

When the heating system is cool, the pressure should ideally be between 1 and 1.5 bar on the pressure gauge (the indicator needle would typically be in the green section). 

If the pressure falls below 0.5 bar (into the red section), water has escaped from the system and needs to be replenished.

Note: The red part of the dial could also signify excessively high pressure (around 2.75 bar or more). 

If the pressure gauge shows high pressure due to overfilling, you’ll need to vent a radiator until the pressure gauge returns to between 1 and 1.5 bar.

If the pressure increases by more than 1 bar when the heating is at full temperature, the expansion vessel may need repressurising.

This task will require a service engineer. 

Typically, the system’s pressure will need topping up once or twice a year. If you find yourself having to repressurise your heating system more frequently, please contact your installer.

What should boiler pressure be when heating is on 

Here’s a summary of the key points to remember regarding your boiler pressure: 

• When your boiler and heating are on, the pressure should be between 1.0 to 2.0 bar. 
• When the heating is off, boiler pressure should be between 1 and 1.5 bar. 

If you need to increase the pressure – add water via the filling loop. 

If you need to decrease pressure, consider venting your radiators. 

Conclusion

If you want to know what pressure an combi boiler should have, remember the following values:

• 0.8 bar – below this pressure, the boiler usually goes into fault mode due to lack of water. You need to fill the boiler with water through the filling tap.
• 1.0 – 2.0 bar – this is the normal operating pressure of the boiler
• 3.0 bar – this is the maximum operating pressure of the boiler.

If your pressure is close to the maxim value, you need to lower the boiler pressure by bleeding a radiator.