Low Boiler Pressure? Here’s How To Repressurise Boilers

Not getting adequate hot water in your home during the cold months? There may be some issue with your boiler pressure. Without constant water pressure, your boiler will fail to work efficiently. 

Low pressure is a clear indication of some underlying issues with your boiler system. So how would you deal with a low boiler pressure?

Low Boiler Pressure? Here’s How To repressurize Boilers?

Steps To Repressurize Boilers 

The first step is to ensure that the drop in your boiler pressure isn’t because of a leak. In case of a leak, you need to contact a professional gas engineer to fix the problem. However, if there are no existing leaks, you can repressurize your boiler using the user manual. 

You can follow our easy steps to repressurize your boiler and get back to the normal 1 bar level. However, if you are not confident enough, we suggest opting for a qualified professional. 

How to repressurize your boiler system –

  • Start with switching off the boiler system and allow some time for it to cool.
  • The filling loop must be checked to ensure that both ends are secured and attached.
  • Open both the valves of the system. You will hear the sound of mains cold water running into the system. 
  • Keep the valves open until you get a pressure reading of 1.5 bar on your boiler.
  • Close the two valves. However, you should close one valve at a time. 
  • Now, switch on your boiler again. Depending on the model of your boiler, you need to press your boiler’s reset button(how to reset a boiler).
  • Reverse the filling loop. Make sure to collect any water remaining in the loop.
  • Clean the filling loop and keep it in a safe place.

How To Use A Repressurize Key 

If you own a repressurize key, then follow these steps –

  • Switch off your boiler system. Wait for a few minutes to allow the system to cool. 
  • It’s time to find the concealed tray present underneath your boiler. Now, locate the slot and key. 
  • Insert your repressurize key into the correct slot. Make sure that the key lines up properly with your system’s open padlock signal. 
  • Push the key firmly and rotate it towards the sign of ‘closed padlock.’
  • You will find a white square nut. Turn it clockwise to ensure the flow of water into the boiler. 
  • Continue the process until you notice a pressure of 1.5 bars.
  • Now, rotate the nut clockwise. Keep rotating until the inflow of water stops.
  • Turn the key back to the initial sign of ‘open padlock.’ However, some water may still come out at this moment. You don’t need to worry about it.
  • Next, turn on your boiler again.

Now that we have covered the repressurizing steps, it’s time to know the process of checking your boiler pressure. 

How to Check if your Boiler Pressure is Low?

Suspecting a low pressure in your boiler? Well, the first step is to check the water pressure gauge located at the front of your boiler. However, different boilers come with different types of pressure gauges. 

You must check the correct information provided by your manufacturer in the user manual. 

Boilers with a digital gauge will represent the pressure in terms of bars. If your boiler screen has a reading of less than 1 bar, it indicates low pressure. Often boilers may display a flash reading or pressure warning to indicate a low-pressure problem. 

Boilers with a hydraulic gauge will display the reading on a dial. The red sections on your dial indicate high and low pressure. If you find the indicator on the left-hand side of the red part, it is a case of low pressure. If the indicator needle is on the right-hand side of the red part, it is a case of high water pressure. 

So, how will you locate the ideal boiler pressure?

What is the Right Water Pressure for your Boiler?

A reading between 1 bar and 2 bar is generally the ideal water pressure. However, in the case of cold radiators, you may see a one bar pressure reading. If you notice a reading below the one bar, it is a case of low pressure, while anything equal to or above 2.75 bars is a case of high-pressure. 

In case of a high-pressure problem, we suggest contacting an engineer to quickly fix the problem. The following may lead to a high boiler pressure –

  • If you accidentally overfill your boiler with water 
  • The pressure release tools of your boiler have become damaged.

Reducing the pressure of your boiler can get dangerous. It is always safe to contact a qualified engineer to help you with a high-pressure boiler. Now that we know the causes of high boiler pressure, it’s time to learn the major causes of low boiler pressure. 

Common Reasons Behind Low Boiler Pressure

There are two common reasons for a low boiler pressure –

  • Bleeding Radiators
  • A leak in the heating system

Bleeding Radiators

Bleeding radiators are a common cause of low-pressure boilers. Releasing all the water from the central heating system of your boiler can cause a pressure loss. However, you can easily increase the pressure by following our repressurizing guide. 

A leak in Heating System

A leak in the central heating system can be another cause of low boiler pressure. This leak in your heating system may be barely perceptible and small. This causes a gradual decrease in your boiler pressure. 

To locate a leak in your heating system, you need to check for damp patches around the boiler, pipes, and radiators. However, refrain from checking the boiler insides to locate a leak as it can be dangerous. You may leave this task with a registered heating engineer.

If you have found a leak, the next step is to contact a reliable engineer. However, if you fail to locate any leaks and the low-pressure problem persists, call out a registered engineer. It will save you time, money, and stress in the long run. 

Still, have questions on your mind about a low-boiler pressure?

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Last Updated on November 6, 2021

Frequently Asked Questions

How Often Should You Repressurise Your Boiler?

To maintain safety, we recommend repressurising a boiler only when the pressure is too low. Check the pressure of your boiler system every few weeks to ensure constant boiler pressure.

If you are frequently repressurising the boiler, it may be a case of a leak in the system. To prevent further damage, we recommend locating the leak and fixing it quickly.

How Long until My Water Pressure Returns to Normal?

The time to repressurise your boiler system will depend on how the existing pressure of your boiler. The lower the pressure, the more will be the time required. However, if there are no leaks in your heating system, it may take around 10 seconds to repressurise it. 

Follow our steps and allow the water to flow into the valves for about 10 seconds. This will be enough for your combi-boiler to get back its original pressure.

Is Low Boiler Pressure Dangerous?

Well, no. There is nothing to panic about a low boiler pressure. The only issue with a low boiler pressure is that you have to survive the cold without any hot water. 

Your heating system will not work properly in case of low boiler pressure. It may also impact your system’s efficiency. Your system will require more time to attain your desired temperature in case of low boiler pressure.

Can Low Water Pressure Damage My Combi-boiler?

No, but it can reduce the efficiency of your combi-boiler. 

You must check the pressure of the water main to ensure the adequate performance of the heating system. Low water pressure will slow down the heating process of your system. If the water main is deprived of adequate water pressure, the system will be starved of cold water. 

Though the low water pressure won’t cause damage to your combi-boiler, it will significantly reduce the effectiveness of the system. It will get difficult to maintain a warm temperature in your home and may lead to more energy costs.


Author: Indra Gupta

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

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