What is a Boiler Filling Loop?

There are many different elements to a boiler, and as a domestic homeowner, it can be challenging to understand which part does what. They all serve a particular purpose to ensure that your property is being heated efficiently and effectively. A boiler filling loop is frequently used to top up the water pressure in your boiler, but what happens if it dysfunctions and it’s not operating to its full capacity? Our guide will take you through the different types and their usage.



What are Boiler Filling Loop Valves?


Central heating filling loops on the surface are hoses that link your boiler to the main water supply on a temporary basis. It helps to depressurise the boiler when bleeding or draining the system whilst topping it up with water.



Where Can I find my Boiler’s Filling Loop?


To locate the filling loop on your boiler, take a look at the underside of the boiler near the pipework – relevant for both external or internal filling loop valves. In some instances, there may be a placement other than the boiler’s underside which can be found on the paper diagram supplied with your product or found online via the manufacturer’s website. Usually we’ll always recommend to contact our boiler repairs team if you notice anything unusual with your system, but if problems arise with the water pressure then it can be an easy fix you can do yourself.





There are two different types of filling loops which have different purposes. An external boiler fill valve or an internal one. These can usually be bought from a highstreet DIY shop or online, but it’s important to make sure you’re getting the right one. If in doubt try specialist plumbing stores and ask for advice and guidance and ensure they have them in stock. Another alternative is to check the manufacturer if you’re in need of a new one.



External Filling Loop Valves


You may be familiar with the braided look of the hose that comes with standard boilers. External filling loops come with compression fittings on both ends of the tubing and must be fitted in a correct fashion for it to function properly and fill up accordingly. At a minimum, there will be a one-stop valve on the loop to control the flow of water. There’s also the double check valve which features two spring-loaded mechanisms and stops water from entering back into the mains.


Internal Filling Loop Valves


In contrast, an internal loop is less common and of a more complex structure. It does however work in a similar way to an external valve and can appear on combi boilers with integrated filling loops that are connected directly to the mains.



How to Use a Boiler Filling Loop


A boiler fill valve and loop operation depend on whether it’s external or internal. For internal loops, there are a number of steps to bear in mind depending on your boiler, so check the manufacturer’s guide just in case. Firstly turn off all electricity to the mains and then open the hatch and slot in the filling loop key.


To top up the boiler and CHS with water you’ll need to activate the system and keep check of the pressure gauge while it reaches the correct range between 1 bar to 1.5 bars. Then repeat this step in reverse, tightening the knob clockwise if you first turned it anticlockwise. Finally, remove the key and if the issue continues to arise then seek professional help from a qualified plumber.


For external filling loops, you’ll need to turn off the boiler first and then reach for the isolation valve and remove the cap. To fit the loop tighten each end using an adjustable spanner, and turn each lever slowly to let water into the boiler. The on/off positions will guide you on the positioning, if it is in a cross or T shape it is off, and if it lines up then it is on.


Again, keep an eye on the pressure gauge between 1 bar to 1.5 bars and close the lever once the pressure level has reached the designated amount. If it does go beyond 1.5 bars then bleed out and start again. When you’re happy with the result, remove the external loop and put the valve cap back on. If in doubt or you feel uncomfortable carrying out this task, seek help from the professionals.



See What CS Boxall Can do for your Boiler


At CS Boxall, we have years of experience supplying, maintaining and installing domestic boilers from a range of leading manufacturers. Our reactive and efficient approach to helping our customers means that we’re reliable, trusted and deliver the results you want. We offer a wide range of plumbing services and are experts in all aspects of boiler fitting and repair. We provide the full package so there’s no need to look elsewhere. Contact us today.