Boiler Pressure Too High? – A Complete Guide

Even if you ignore it, a boiler is an important part of your daily life. This is a device that keeps your water and central heating system in place. It also maintains the water pressure inside your heating system. This silent device makes sure that the pressure is either too high or too low.

Still doesn’t seem interesting? Well, when the pressure in your heating system goes haywire, you will have to notice. If this happens or your boiler breaks down, you won’t get any hot water and no heating. Then, you have to take the necessary steps to get your boiler system fixed.

If the question “Is my boiler pressure too high?” has popped into your head, here’s how to handle the situation.

What Is Boiler Pressure & Why It’s Important? 

In simple terms, boiler pressure is the balance of water and heat within your central heating system. This pressure needs to be perfectly balanced for the boiler to pump hot water for you. If this pressure is too high, your heating system will be overworked and the inbuilt safety mechanism will trigger a lockout.

If the pressure is too low, then the system won’t work properly as well. Let’s take a look into this in detail.

Is low boiler pressure dangerous?

You don’t have to panic if the pressure is too low in your boiler. It won’t cause any damage to your boiler. But a lower boiler pressure will affect the efficiency of your central heating system. The water from the system may not heat properly. This might not keep your house as warm as it used to be.

The most common cause of a low boiler pressure is a leak in the heating system. Or, bleeding your radiators may also cause this issue.

Doing this in heating systems removes any air in it, which causes the boiler’s pressure to drop. Now, take a look at the other issue.    

Is high boiler pressure dangerous?

No, is not as dangerous as it seems. Even if the boiler pressure is too high, your system has a pressure relief valve to take care of it. In that case, the boiler will turn itself off and the pressure relief valve will handle the boiler’s pressure. So, you need to keep an eye on it.

But in such a situation, leaving the boiler as is not a good idea. Get a trained heating engineer to check your boiler’s pressure gauge.

Is Your Boiler Pressure Too High?

To keep your heating system intact, you need to check if the boiler’s pressure is too high or not. A small increase in the heating system’s pressure is fine, but sometimes it may get over-pressurised.

There is an expansion vessel that controls the boiler pressure. This also balances the air and water in the heating system. If the air inside this vessel is too less, the boiler pressure will become high. Similarly, too much air in the vessel can also cause the boiler pressure to spike up rapidly.  

What Is The Ideal Boiler Pressure?

To check the boiler pressure, you need to check the pressure gauge. You will find a red and green mark, indicating low and high boiler pressure respectively. The ideal boiler pressure must be between 1 bar and 2 bar. The safest marking is between 1 and 1.5 bars – the green zone – on the pressure gauge.

You may have a combi boiler. A combi boiler pressure having a reading of 1.5 bar and more while the heating is going on, is perfectly normal. This reading goes beyond 1.5 bars because of the water demand on the boiler.

So, a boiler pressure reading between 1.5 to 2.5 bar is not something you need to worry about. When the boiler pressure is too high, say 3 to 4 bar, then you need to be worried. Get a heating engineer immediately to fix your boiler.

There are other things you need to keep in mind. If your boiler is giving off high pressure readings frequently and is over 10 years old, you have to get a new boiler. Furthermore, if the boiler is shutting down irregularly and not turning on, you have a problem. Sometimes, your boiler pressure will be in the red zone, i.e. 3 bar or 4 bar, and continue working. That may seem to be good news, but you still have to get it checked by a professional.

Things That Can Affect Boiler Pressure

If you think that the boiler pressure is too high or too low, you need to first check the pressure gauge. Check if the boiler pressure is too high or you have set it to a higher pressure. If you aren’t satisfied after checking the boiler pressure gauge, there may be other factors affecting your boiler pressure.   

Boiler Heating System Has Been Overfilled

A common cause for your boiler pressure to increase rapidly is an overfilled heating system.

Your boiler needs a sufficient amount of water to work smoothly. So, there is an external filling loop that brings in the water for the boiler. This loop fills water using two valves. If there’s too much water in the system, it adds more pressure to the boiler.

But sometimes, the water overfills the heating system and puts huge pressure on the boiler. This leads to high boiler pressure, which can damage your pump seals and copper joints.

How to Fix This?

You have to drain the water from your boiler to lower its pressure. You have two options to do this –

  • Using the radiator bleed valve
  • Using the drain cock

In the first method, get some towels and a bucket to handle the water. While bleeding the radiator, shut off the valve at 1.3 bar and collect the water using the bucket. This way, you can prevent reducing the pressure too much. A radiator key will help you in this process.

In the second method, you have to connect a small hose to the drain cock. Then, you have to open the valve to let the water go. Ask someone to help you with checking the boiler reading. When the reading gets around 1.3 bar, switch off the tap.

Boiler Pressure Rises

There may be a situation where the boiler pressure rises above 0.3 bar when you have turned the heating on. While a rise in boiler pressure of under 0.3 bar is okay, you might have a problem if you see that the pressure goes above 0.5 bar.

You already know that there are pressure-release valves and expansion vessels to let go of the pressure. If these units are not working properly, they don’t release the pressure. Instead, they contain it, and that is why your boiler pressure may rise irregularly.

How To Fix This?

You need to need to release this extra boiler pressure. So, you have to contact a boiler engineer to check your combi boiler pressure. He or she will check your boiler pressure gauge, pressure relief valve and fix it.

Boiler Pressure Rises When Heating Isn’t On

This can happen if the filling loop, which is used for increasing the boiler pressure, isn’t properly turned off. If the pressure release valve is partially open, this might leak small quantities of water into

your system. This will increase boiler pressure even if you didn’t turn on the heating.

How To Fix This?

You have to detach the filling loop of your boiler. For that, you have to consult a professional who will disconnect it for you. Doing this will reduce the boiler pressure and wouldn’t let much water get into your boiler.   

Common Error Codes for High Boiler Pressure

Lets us now look at some common error codes and their fixes.

  • E133 – This means that your boiler hasn’t been ignited. You need to reset the boiler to fix this.
  • EA 227 – This indicates that the Worcester Bosch boiler has been switched off. A simple boiler reset will fix this.
  • E110, E125, and E131 – These error codes are telling you that the boiler is overheated. Bleed the radiators and reset the boiler to resolve this problem.
  • F1 – This one’s for the Ideal boiler brand, indicating that your boiler’s pressure is low. You can make the error code vanish by adding water to increase your boiler pressure.

It is recommended that you get immediate professional help whenever you see an error code pop up.  

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

Even if it seems impossible, there are ways to reduce boiler pressure and handle the situation.

Bleed radiators

This will release excess air from your system. It’ll also lower the water pressure and remove too much water. So, open the valve gently, but make sure you place buckets underneath it to collect the extra water.

Use a drain-off valve

Locate the drain-off valve also called drain cock and like the previous step, place a bucket below it. Then, slowly open the valve, while checking the reading on the boiler pressure gauge. When the reading reaches 1 bar, close it.

Open up your filter valve

In such a high pressure situation, you have to check your filter valve. If your heating system has one, open it and place a tub or a bucket under it. You can close this valve when the boiler pressure gauge reaches 1 bar.

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Last Updated on November 7, 2021

Frequently Asked Questions

Will My Boiler Explode?

Modern boilers are designed to tackle excessive pressure up to 20 PSI. If the pressure release valve fails and the amount of pressure goes beyond this level, your boiler might fail. Such high pressure may cause your boiler to explode.

So, if you feel that your boiler is overheated or over-pressurised, contact a boiler engineer.

Do Bleeding Radiators Reduce Boiler Rressure?

Yes, it does. When you bleed a radiator, the excessive air trapped in it is released. This reduces your boiler’s pressure.

How Often Should You Repressurise A Boiler?

Usually, you can repressurise the boiler one or two times a year. You have to keep a tab on it. When the system is cold, the pressure will be around 1 to 1.5 bar. It may sometimes fall below 0.5 bar too. If you feel the pressure fluctuates too much, you may need to top it up more often. In such cases, contact a heating engineer.


Author: Indra Gupta

Indra is an in-house writer with a love of Newcastle United and all things sustainable.

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