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Winter Weather Advice: Understanding boiler pressure

Boilers are at the heart of your home, providing your living space with heating and hot water. Keeping your boiler on the perfect setting can be difficult due to the constant internal and external factors that impact the pressure.

However, our experts are here to help you understand how to stay on top of your boiler pressure.

Repressurising a boiler is a relatively simple process and can be completed in two ways via an external or internal filling loop.

External filling loops are located on the outside of the boiler and usually have a silver braided hose with either one of two fillings taps. The process is slightly different for external filling loops depending on if there are one or two taps.

For one tap, all you need to do to repressurise is:

Twist the tap gently until you hear the water flowing, you may not need to open it fully.

Wait for the pressure to reach 1.5.

Once it reaches 1.5, close the tap again.


A two tap external filling loop is used in the same way as above; however, one of the taps should be opened fully before gently opening the second tap to hear the water flowing

On the other hand, the process for internal filling loops is a little bit different. The internal filling loop is located underneath the boiler, and the two taps are located on either side, with one on the left and the other on the right.

How to repressurise them is like a two-tap external loop but remember to turn the right tap open first and follow it up by twisting the left tap slowly.

What pressure should your boiler be at?

For most boilers the pressure should typically be between 1-2 bars. However, what you are targeting when repressurising is around 1.5 bars. If there is a fault in your boiler there are various codes that could appear on your dial.

You can see what each code means here.

How to decrease boiler pressure?

On the other hand, boiler pressure can also get too high and will need urgent action when it is too high. High boiler pressure can occur because of high water levels, or failure of internal boiler components.

The way you can tackle a boiler that has too high pressure is to is by: 

Switch off your boiler and wait for it to cool.

Bleed the radiators to release any air.

Read our step-by-step guide on bleeding your radiators.

Check the boiler pressure and if the pressure is still high use a radiator bleed valve to drain some of the water into a jug.

Check and made sure the tap(s) on the filling loop is fully closed.


If you take these steps but your boiler pressure still rises, it’s important to contact your local installer as soon as possible to fix the problem.

You can read more about how to repressurise your boiler here.

Looking for a new boiler for your home?

Glow-worm manufactures and supplies a complete range of boilers for your home. Look at our combi, system or heat-only boilers page for more information.