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Water pressure: External filling loop

How do I top up water pressure?

Combi and system boilers and your heating system work under pressure. If the pressure drops below a certain level the boiler will not fire (start).

Combi and system boilers need a minimum pressure within the system to work. Leaks in the system will cause your boiler to lose pressure. Leaks can be very small and you may not be able to see them. It is easy to solve this loss in pressure by topping up your system - your installer will be able to do this quickly. However, it is essential they also find and fix the leak.

It is a good idea to regularly check the pressure gauge to make sure there are no tiny leaks within your system - ask your installer to show you how if you’re not sure. You can find the correct pressure levels for your boiler and instructions for repressurising the system in the user instructions. If you are in any doubt, we recommend you ask a competent person, such as an installer to repressurise your system for you.

We have images and intstructions below for an ecoTEC pro with an external filling loop which may be useful. If you have another boiler then please search for your boiler model in the questions bar above and click "ask" to find out more specific information about your appliance water pressure settings.

We also have a comprehensive set of self-help videos on our youtube channel which you can get to by clicking here.

The boiler should read between 1 to 1.5 bar of pressure when the central heating is cold. If this drops too low, below 0.5 bar for example, this normally means water has been lost from the central heating heating system and the filling loop must be used to replace this water. When the central heating is on, the pressure may increase on the boiler, however the pressure generally must not increase by more than 1 bar. If this is the case it could indicate an internal component of the boiler called an Expansion Vessel may need pressurising. A service engineer will need to be contacted in this case.   

This appliance doesn't come with an integrated filling loop. There should be an external filling loop fitted to the system by your original installer. This will either be located below or around the boiler area or in the cylinder cupboard. Although there are many variations on what a filling loop will look like they will all carry out the same function so will look broadly similar. Two examples of external loops will look like the pictures below and connect across two separate pipes:

This type of filling loop has two taps on it.  You would open one fully then slowly open the other until you start to hear water passing through.  Once you hear water passing through keep an eye on the boiler's gauge, pressure reading or external pressure gauge and close the valve when it reaches 1 - 1.5 bar.   

This type of filling loop only has one tap on it:

With this type you would slowly open the tap until you start to hear water passing through. Once you hear water passing through keep an eye on the boiler's gauge, pressure reading or external pressure gauge and close the valve when it reaches 1 - 1.5 bar.