Filling Loops

Top up system pressure the right way with our range of boiler filling loops. Used to safely connect the mains water supply to sealed heating systems, a filling loop is essential for refilling or repressurising during installation and maintenance. We stock a range of boiler filling loops, including built-in, external and double-check valve options to meet current regulations. Suitable for use with most combi and system boilers, filling loops are a straightforward solution for keeping pressure levels where they should be.

Q: What is a boiler filling loop and what does it do?

A: A boiler filling loop is a pipe and valve assembly used to connect your boiler to the mains water supply. It allows you to manually top up the water pressure in sealed central heating systems – especially in combi boilers. Once the correct pressure is reached, the loop should be disconnected or the valves closed to maintain system safety.

Q: What types of filling loops do you stock?

A: We stock a range of boiler filling loops, including:

• Standard filling loops for sealed system boilers.

• Double check valve filling loops for backflow prevention.

• Pre-assembled kits with isolation and check valves.

• Altecnic filling loops for trusted performance.

Whether you're replacing a faulty part or setting up a new boiler install, you'll find reliable options to suit most systems.

Q: Where is the filling loop on my boiler?

A: The filling loop is typically found underneath the boiler – either as a flexible braided hose connected between two valves, or as an internal loop within the boiler casing. For combi boilers, this is usually just below the control panel. If you’re unsure, check your boiler manual or consult an installer. 

Q: How do I use a filling loop to increase boiler pressure?

A: To top up pressure:

1. Make sure the boiler is cool.

2. Locate the filling loop and open both valves slowly.

3. Watch the pressure gauge – most systems need 1.0 to 1.5 bar.

4. Close both valves once at the correct pressure.

5. Restart the boiler if needed.

Never leave the filling loop open – it can cause over-pressurisation.

Q: Should the filling loop be open or closed?

A: The filling loop should remain closed at all times, unless you're actively topping up the system pressure. Leaving it open risks overfilling the system and may lead to leaks or pressure relief valve discharge.

Q: Can I repressurise my boiler myself?

A: Yes, repressurising a boiler with a filling loop is usually a straightforward DIY job. Just follow the steps in your boiler manual or use the guide above. If pressure drops frequently or won’t rise, there may be a fault elsewhere in the system – such as a leak or faulty expansion vessel.

Q: Do you stock combi boiler filling loops?

A: Yes – our filling loops are suitable for use with most combi boilers as well as other sealed systems. We also supply replacement valves, fittings, and loop assemblies for quick maintenance and installations.

Q: What is a Tiger Loop or internal deaerator?

A: While not a filling loop, a Tiger Loop is a deaerator used in oil heating systems to remove air from the fuel supply. It's designed to improve burner efficiency and reduce issues caused by air in the oil line. These are commonly used in off-grid oil boiler setups.

Q: Do you deliver boiler filling loops across the UK?

A: Yes – we offer UK-wide delivery on all boiler filling loops, valves and accessories. You can also collect from your nearest JT Atkinson branch for fast, local service.