Boiler Filling Loop Guide UK: What It Is & How to Use It Safely

What is a Boiler Filling Loop? A Complete UK Guide

A boiler filling loop is a small pipe that helps add water to your boiler system. It connects your main water supply to your boiler. You use it when the boiler pressure is too low. This helps the heating system work properly. Most UK homes with combi boilers have a filling loop. It is usually found under the boiler or close to the pipes. In this guide, you will learn all the key details about what a filling loop is, how it works,  and how to use it safely in your UK home.

What is a Boiler Filling Loop?

A boiler filling loop is a small pipe that connects your boiler to the main water supply. It is used to add water when the pressure inside the boiler is too low. If the pressure is low, your central heating may not work properly. The filling loop helps fix this problem.

This helps your central heating system to work properly. You use the filling loop only when you need it. You open the filling loop valves to let water in and watch the pressure gauge. The pressure gauge shows the water pressure.

It is found in many homes in the UK, especially with combi boilers. The filling loop is usually under the boiler or near the pipes. It helps keep your heating system working safely, so your home stays warm and comfortable.

Boiler Filling Loop Guide UK

How Does a Filling Loop Work?

A filling loop works by allowing water from your mains supply to go into your boiler. It is used when the water pressure inside your boiler drops too low. Low pressure can stop your central heating from working properly. The filling loop is a small pipe with two taps or valves. These taps are usually closed. When the boiler needs more water, you open both taps. This lets water flow through the pipe and into the boiler.

As the water goes into the boiler, you should look at the pressure gauge. This gauge shows how much pressure is inside the system. When the pressure goes up to the right level (usually between 1 and 1.5 bar), you need to turn both taps off. This will stop more water from going in. After that, your boiler will have enough water to work properly again.

The filling loop is only used when the pressure is low. You should not leave the taps open all the time. That could cause too much pressure, which can damage the boiler. So, it’s important to open the taps only when needed and close them right after. This keeps your heating safe and working properly.

Main Types of Filling Loops for Boilers

Here are two types of loops. Both are used to add water to your central heating system when the pressure is too low.

 External Filling Loop

An external filling loop is the most common type used in many UK homes. It is a short silver pipe that you can see under or near the boiler. This pipe connects the mains water supply to your boiler system. It has two small taps or valves. These taps are usually turned off. When your boiler pressure is too low, you turn both taps to let water into the boiler. This type of filling loop is simple to use.

Internal Filling Loop

An internal filling loop is already built inside the boiler. You don’t see any separate pipes.
Instead, there may be one or two small handles or dials on the boiler itself. When your boiler pressure is low, you turn these handles to let water into the boiler. The water flows in through the hidden pipe inside the boiler. When the pressure is correct, turn the handles back to stop the water.

Where is the filling loop on my boiler?

The filling loop is usually found just under the boiler, near the pipework. It is a small silver or grey pipe that connects two pipes together. It can be straight or shaped like a loop. You will also see two small taps or handles on both ends of the pipe. These taps are used to let water into your boiler if the pressure is too low.

The filling loop is a main part of your central heating system. It helps you add water when your pressure gauge shows the pressure is too low. Keeping the right pressure helps your boiler work properly and keeps your home warm.

Sometimes, the filling loop is found behind a small cover under the boiler. You can carefully open the cover to see the pipe and small taps. In some new boilers, the filling loop is inside the boiler. You won’t see a pipe. Instead, there are small handles or dials on the front or side of the boiler.

If you are not found where the filling loop is, the best way is to look in your boiler manual. It will show pictures or steps to help you find it. You can also ask a heating engineer if you need help.

Guide: How to use an internal filling loop

An internal filling loop is already built inside the boiler. This means you will not see a separate pipe like the external filling loop. Instead, you will see one or two small handles, dials, or levers on the front, side, or bottom of the boiler. These controls are used to add water to your boiler when the pressure is low.

To use it, first check the pressure gauge. This gauge shows how much pressure is in the system. If the pressure is below 1 bar, it is too low, and you need to increase the pressure. Now, slowly turn the handle or dial on the boiler. This will open the filling loop inside. You may hear the sound of water going into the boiler. 

When the pressure goes up to the correct level. you must stop the water. After that, your boiler now has enough water pressure to work well. Your central heating should start working again and heat your home properly.

Guide: How to use an internal filling loop

An internal filling loop is already built inside the boiler. This means you will not see a separate pipe like the external filling loop. Instead, you will see one or two small handles, dials, or levers on the front, side, or bottom of the boiler. These controls are used to add water to your boiler when the pressure is low.

To use it, first check the pressure gauge. This gauge shows how much pressure is in the system. If the pressure is below 1 bar, it is too low, your radiator is not working, and you need to increase the pressure. Now, slowly turn the handle or dial on the boiler. This will open the filling loop inside. You may hear the sound of water going into the boiler. 

When the pressure goes up to the correct level, usually between 1 and 1.5 bar, you must stop the water. After that, your boiler now has enough water pressure to work well. Your central heating should start working again and heat your home properly.

How to Add Water to Your Boiler with the Filling Loop

Here are the simple steps that show how to add water to a boiler with a filling loop:

• First, look at the boiler screen to see if the water is low. If the level is low or the number is under 1, you need to add water.
• Find the two small taps or handles under the boiler. These are part of the filling loop that lets water into the boiler.
• Turn both taps slowly; this lets water go in. This lets water flow from your home’s water pipe into the boiler.
• You may hear water moving inside the boiler. This is a normal sound that means water is going in.
• Watch the needle or number rise on the front screen. There will be a number or pointer that shows the water level rising.
• When it reaches between 1 and 1.5, stop adding water. This means the boiler now has enough water to work well.
• Turn both taps back to the off position. This stops the water from flowing into the boiler and keeps the boiler safe.
• Make sure both taps are fully turned off. If even one is open, it could cause a leak or other issues.

Now your boiler has enough water and should work properly again.

Conclusion:

A boiler filling loop is a small but important tool. It helps you add water to the boiler when the pressure gets too low. This helps the boiler work properly. Whether your loop is inside or outside the boiler, the steps are simple. Just turn the taps slowly, let water flow in, and stop when the level is right.

Keeping the right water level helps your boiler work well and keeps your home warm. Always turn the taps off when you’re done. If you’re unsure, check your boiler guide or ask a heating expert for help.

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FAQs:

How do I find my filling loop?

You can find your filling loop by looking under or near your boiler. It’s usually a small silver pipe with two small taps or handles. If you can’t see it, check inside the boiler if you have an internal loop. 

What is the purpose of a filling loop?

The purpose of a filling loop is to add water to your boiler. It helps increase the pressure when it gets too low, so your heating and hot water work properly.

How to connect the filling loop on the boiler?

To connect a filling loop, attach both ends of the pipe to the boiler valves. Make sure both valves are off before starting, then turn them on to let water flow in.

What happens if the filling loop is left open?

If the filling loop is left open, too much water can go into the boiler. This can make the pressure too high and may damage your boiler or cause leaks.

Should the Filling Loop be connected permanently to the Boiler? 

No, the filling loop should not stay connected all the time. It’s best to remove it after use to stop leaks and keep your boiler safe.