BFL's are what your friends will know them as. Boiler filling loops are not totally pointless and here's why.
Do you want to know exactly what a filling loop valve is?
Your filling loop is commonly used to top up your boiler's water pressure, so you may want to know where it is and how to use it.
Whatever the case is, we have you covered with a detailed look at filling loops and their valves in this easy-to-digest, jargon-free guide.
We've also included a very easy-to-follow and quick video guide from our boiler expert.
PS We fit new boilers with gas installation nationwide. Simply answer these questions, get your fixed price and you could get it installed as quick as tomorrow.
What are Filling Loop Valves?
Boiler filling loops are hoses that can be used to hook up the main water supply to your boiler on a temporary basis.
Its basic purpose is to repressurise a boiler and top it up with water when draining or bleeding the system.
Check out our video tutorial below if you are interested in knowing how to use your boiler's filling loop to top up the pressure.
Defining Filling Loop Valves
As for the actual filling loop valves, these usually come in the form of a double check valve and stop valve, each positioned at one end of the filling loop.
The exact makeup of a filling loop valve will depend on the type in question.
Types of Filling Loops
Let’s now take a closer look at the two main categories of boiler filling loops and their valves…
External Boiler Filling Loop Valves
Generally, this type of filling loop features a braided hose that comes with compression fittings on either end.
There’ll be a minimum of one-stop valve present on this type of filling loop. The stop valve is a means of controlling water flow through the loop.
Beyond that, you have the double check valve which gets its name from the fact that it comprises two spring-loaded mechanisms. This valve with these two anti-backflow mechanisms is used to stop water back flowing into the mains.
When an external boiler filling loop is fitted, it must be installed in the correct way. Failure to do so will stop the system from filling up as it should.
Internal Filling Loop Valves
Next, we have the internal version of boiler filling loops. These filling loops are less common. These filling loops have a more complex structure but work in essentially the same way.
Internal filling loops and their valves sometimes appear on combi boilers such as Viessmann's range which comes with integrated filling loops.
Combi boilers come with a direct mains connection meaning that the filling loop might tee off from this connection.
Buying a Filling Loop Valve
Filling loops and filling loop valves can usually be purchased at a local hardware store. Online retailers might also suffice. Of course, it’s essential that you get the right valve.
If you’re finding it difficult to find the correct filling loop or valve for your boiler’s filling loop, try plumbing and heating specialist stores.
It would be worth calling up the store(s) you intend to go to beforehand. This way you can check whether they have the specific filling loop or filling loop valve you need in stock. You could also try contacting the manufacturer of the relevant products.
Where is Your Boiler's Filling Loop?
Your filling loop will be near the pipework, generally on the underside of the boiler. This would be the case whether it’s an internal or external filling loop.
It should be noted that some filling loop products may have a placement other than the boiler’s underside.
If in doubt, find a paper diagram (if you have one) or the online diagram of your combi boiler filling loop or central heating filling loop.
The latter should be provided on the manufacturer’s website. If you can’t find it, try getting in touch with the manufacturer.
Assuming you already have the filling loop installed, you’ll be glad to know that handling a filling loop and its valves is generally something you can take on DIY.
If your boiler’s pressure is low, you can repressurise your central heating system (CHS) and boiler fairly easily.
How Do You Use a Boiler Filling Loop?
The exact process of using a filling loop depends on whether it’s internal or external…
Internal Filling Loops
To use an internal filling loop to repressurise your boiler and CHS, you’ll need to follow several steps.
You should be aware that for each of these steps, what is exactly needed will depend on your specific boiler. Check with the manufacturer’s guidance if in doubt.
First, turn off the boiler and turn off all electricity in your home at the mains. This first step is essential for safety reasons. Next, open the boiler hatch/flap and insert your filling loop key in the relevant slot.
You may then activate the system. What exactly activating the system will involve will depend on the boiler in question.
In some cases, you’ll need to turn the key to the ‘closed padlock symbol’ before turning the knob next to it anticlockwise.
This would allow you to top up the boiler and CHS with water. If in doubt, follow your manufacturer’s instructions or/and contact them directly. It’s never safe to simply guess what must be done when working with a boiler.
Once you’ve activated the system per the manufacturer’s guidance, keep an eye on the pressure gauge until it’s in the correct range.
This should be around 1 bar to 1.5 bars (although again, you should double-check what the manufacturer of your boiler recommends).
Once the pressure gauge is in the ideal range, repeat the steps for activating the system but in reverse (e.g., if you tightened the knob anticlockwise, then tighten it clockwise and if the key was turned to the closed padlock, turn it back to open padlock).
You may then remove the key. If the issue keeps repeating, it’s likely there is a leak somewhere and you should hire a qualified professional to take a look at this as soon as possible.
External Filling Loops
Again, for using this type of filling loop, if you have any doubt, check the manufacturer’s guidance for clarity.
Should you have this type of filling loop instead, you’ll first need to turn off the boiler. Then remove the cap from the isolation valve.
Next, fit the external filling loop. The nature of this third step may depend on the filling loop and boiler in question.
Check your manufacturer’s guidance for what must be done here. An adjustable spanner may be needed to tighten each end of the filling loop if necessary.
Make sure to double-check how the valves are positioned to ensure there are no problems. Again, you can check the manufacturer’s instructions for clarity regarding your specific filling loop and boiler.
Then turn the knob (or lever) of the filling loop slowly to allow water into the boiler. The filling loop will have on/off positions.
These determine whether the knob/lever is perpendicular (creates a cross/T-shape) and therefore in the off-position or if it lines up and therefore in the on-position.
Keep an eye on the pressure gauge. The ideal range should again usually be between 1 bar and 1.5 bars.
Turn the knob or lever closed again once the pressure gauge is in the range you want it to be. Should it go past 1.5 bars (or whatever the right range is for your specific boiler), bleed out the radiator and return to the first step.
When everything is good, remove the external filling loop and put the isolation valve cap back in place. A small clean-up may also be needed at the end.
Installing a New Filling Loop
If you’re installing a new filling loop, the exact process will depend on the type in question (i.e., internal or external).
On the one hand, combi boilers generally come with internal filling loops fitted, meaning you don’t have to install anything. Generally, this will have been dealt with already by the installer.
However, system boilers or fuel-burning boilers require external filling loops. These need to be fitted manually.
While internal filling loops generally stay connected on a continuous basis, an external filling loop should only be hooked up to a boiler when needed.
Otherwise, it should be turned off and disconnected until it’s required again. This is in relation to boiler-filling loop regulations.
Note: When a filling loop is connected to a boiler and mains, the risk of backflow (whether the filling loop is in the on or off position) is always present.
Since your neighbours would draw their water from the same source as you, backflow poses a serious and costly risk to not just you but to other properties nearby.
In such a scenario, you could face fines. So, you really should keep your external filling turned off and disconnected unless you’re using it.
For safety, you need to turn off the boiler and turn off the water mains before hooking up an external filling loop.
Installing a Filling Loop
Here are the steps involved in installing a filling loop:
First, you’ll need to inspect the filling loop. Most filling loops feature two valves, but others have just one. Beyond that, the valve types can differ. Some filling loops come with a single control valve along with a double check valve whereas others have two control valves. If in doubt, check your manual.
Given how the filling loop valves are placed, they cannot be interchanged in terms of their use. One valve allows the water to enter with the other allowing the water to exist. You should attach the end such that the stop valve is close to the main lines. The specifics of this step, however, will depend on the manufacturer’s guidance. So always double-check what they recommend before proceeding.
Next, an adjustable spanner will generally be needed to secure the filling loop with the boiler and the mains. Again, check with the manufacturer’s guidance for this step as it may differ depending on the boiler in question.
Once both ends are hooked up correctly, double-check everything is in place correctly per the manufacturer’s guidance.
What we’ve described above is a more detailed description of how to hook up an external filling loop, which we touched on in the previous section.
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