central heating

Your Handy Guide To Boiler Filling Loops

Oct-2020 / 6 min read

Reading Time: 6 minutes

Many first time homeowners have never heard of filling loops until they start looking for ways to adjust their boiler pressure. And that is a part of the process, as you learn more about maintaining your central heating – you get to know every obscure part and their role in the system. 

Plumbingforce prepared this handy guide to help you get to know your boiler filling loops. Here we cover the following points:

  1. What Is A Boiler Filling Loop?
  2. Different Types of Boiler Filling Loops
    • External
    • Internal
  3. Where Can You Buy A Filling Loop?
  4. Where Is Your Filling Loop Located?
  5. How Do You Install A Filling Loop?
    • Inspect Your Filling Loop
    • What Goes Where
    • Secure Your Connection
    • You Are Ready To Go!
  6. How Do You Use A Filling Loop?
    • Using An Internal Filling Loop
    • Using An External Filling Loop

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What Is A Boiler Filling Loop?

A boiler filling loop is a hose that can temporarily connect your boiler to your main water supply. It is used to  repressurise your boiler and top up the water when you drain or bleed your system. They usually come as an additional attachment with the boiler. When they aren’t, you can easily buy it separately.  

Different Types of Boiler Filling Loops

There are 2 types available: 

External Filling Loop

An external filling loop hose is braided with compression fittings on each end. There are also two valves: one to control the water flow (stop valve) and the other to ensure the boiler water doesn’t go back to the mains (double check valve). A part of the external fitting loop connects to your main water line, and the other connects to your boiler. You need to make sure you have the right end on its designated terminal. 

You can easily find an external filling loop in local hardware stores and online retailers. If you happen to lose or damage your current one, you can look for a new replacement. It shouldn’t be too hard to find.

Internal Filling Loop

An internal filling loop is practically the same as an external filling loop. You can typically find internal filling loops in combi boilers. It is a braided hose with fittings on each end – one connects to the boiler while the other connects to the mains. However, there are several standout differences.

Since it is internal, it is fully integrated into the boiler system. The connections are close to one another, so most internal filling loops are shorter than external ones. The hose can be braided, but some models forgo this and simply have a pipe connecting the boiler and water mains with the proper fittings and valves. 

Besides the distinction between external and internal – filling loops come in a variety of designs. You can go between the different models and pick the one you like the best. At the heart of it all, it does the same job. As long as it is high quality, you shouldn’t have a problem with it. 

Where Can You Buy A Boiler Filling Loop?

You can easily find a filling loop in your local hardware stores. If you are having a tough time finding a filling loop, you can try to target plumbing and heating speciality stores. Ones that cater to professional plumbers and heating engineers are bound to have stock ready. 

If you are looking to buy online, you can find excellent options at these retail websites: 

  1. Amazon.co.uk
  2. Ebay.co.uk
  3. Screwfix.com
  4. Wickes.co.uk
  5. Directheatingsupplies.co.uk
  6. Thehardwarestores.co.uk

With these websites, you are sure to find a filling loop for your boiler. 

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Where Is My Filling Loop Located?

Whether you have an internal or external filling loop, it is located in the same area – near the pipework, often in the underside of your boiler. Some brands and models might have a different placement. Suppose you want to have a better idea of where your filling loop is located. In that case, you can try to check out the central heating filling loop diagram or combi boiler filling loop diagram online. With a proper illustration, you don’t have to fumble your way to the isolation valve. 

How Do You Install A Filling Loop?

When it comes to the installation of your filling loop, it depends on what kind you have. An internal one is very different from an external one. However, it shouldn’t be too difficult to identify. For the most part, you can tell by what type of boiler you have.
For example, combi boilers usually have internal filling loops, so there is no installation necessary. Your plumber or heating engineer should have that taken care of for you. 
On the other hand, if you have a fuel burning boiler or a systems boiler you have to install your external filling loop manually. Unlike the internal one that usually stays inside the boiler indefinitely, an external one should only be connected when used. When it isn’t –  it should be turned off and disconnected until the next time you repressurise your boiler. 
Why? Because of the boiler filling loop regulations. When your filling loop connects your boiler and mains there is always a chance for a backflow – it doesn’t matter whether your boiler filling loop is in on or off position. It doesn’t minimise the risk. 
Plumbers, heating engineers, and maintenance codes tend to be very cautious when it comes to backflow because it can lead to water contamination in the main lines. And since the whole neighbourhood draws their water from the same source, this can lead to very serious and very expensive problems. Avoid the fines and only bring out your filling loop when necessary. 
With the warning out of the way, here are step-by-step instructions for installing your filling loop: 

Inspect your filling loop.

See what kind you have on hand. While most models have 2 valves, some only come with one. Even the types of valves may vary. Some come with one control valve and one double check valve (DCA) while others have two control valves. Your manual can be a reference.

What goes where. 

Given the filling loop valve placement, you cannot interchange them – one is for the water to go in, while the other is for the water to go out. Fit the end with the stop valve near the main lines. 

Secure your connection.

Use an adjustable spanner to secure the connection between the filling loop, the boiler and the mains.

You are ready to go!

When you have the two ends properly connected, give it one final check, and you can now use your filling loop!

How Do You Use A Filling Loop?

Installing and using a filling loop is very DIY-friendly. In fact, it is one of the few things you can handle every couple of months. Instead of waiting for your local heating engineer to pop by, you can add this to your list along with other maintenance tasks.
If the pressure is too low or keeps dropping, repressurising your boiler and central heating system is very easy. Here are helpful steps you can take:

Using An Internal Filling Loop

  1. Turn off your boiler or shut down the electricity.
  2. Bring out the key for your internal filling loop.
  3. Open the hatch/ flap and insert the key in its proper slot.
  4. Activate your system. This step may vary according to your boiler. For example, Worcester Bosch, you turn the key from the open to the closed padlock symbol, then turn the knob beside it counterclockwise to top up the water.
  5. Check the pressure gauge until it reaches the right range, usually 1-1.5 bar (keep it green). 
  6. Tighten the knob (clockwise) and turn the key to the open padlock position. 
  7. Remove the key. 

Using An External Filling Loop

  1. Turn off your boiler.
  2. Remove the cap of your isolation valve.
  3. Fit your external filling loop. This part may depend on your set up. Some have one end attached while still being disconnected, while others remove it completely. Use an adjustable spanner to tighten both ends. 
  4. Double-check the position of your valves so that there are no issues. You can consult the manual for this part.
  5. Turn the knob/lever of the filling loop slowly to let the water in the boiler. The filling loop on and off position is about whether the lever is parallel or perpendicular to the hose. If it lines up, then that is the filling loop on-position. If it creates a cross or “t” shape, it is the filling loop off-position. 
  6. Check the pressure gauge. Make sure it is in the 1-1.5 bar range (green) before turning the lever to close. If it goes past the ideal range, just bleed your radiator and go back to step no. 1. 
  7. Disconnect your external filling loop and clean up. 

No matter what type of boiler you have in your home, a filling loop is an easy way to fix your boiler’s pressure. By keeping the pressure at the proper range, you not only get an efficient boiler, but you also minimise the damage on your pipes.
In fact, this is one of the main tasks of your boiler service! Repressurise your boiler! If you need a new boiler installation or additional help with your combi boiler’s filling loop you can contact Plumbingforce at 0330 173 9039
Alternatively, you can also book our services online! We have an excellent team of heating engineers and plumbers who are ready to help you get your central heating in tip-top shape. From brand new installation, regular maintenance and boiler repairs, to emergency call-outs – Plumbingforce can be your one-stop-shop!

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