Filling Loops

A boiler filling loop is a specially-designed component that enables an engineer or property owner to top up system pressure by temporarily connecting the boiler and the property's mains water supply.

The connections are only temporary because water regulations state that water cannot flow back into the mains. If this were to happen, the same water that filled radiators would come out of the taps/shower and could be contaminated.

A boiler filling loop is primarily used to top up the system's water pressure. Water pressure can drop below its desired level if there is a leak, a boiler fault, or if the radiators have recently been bled. As a general rule, the water pressure in a boiler should be between one and two bar.

There are two principal classes of boiler filling loops to be aware of: external and internal. Both types are usually found directly underneath the boiler.

External filling loops are the most-common type and are attached and connected to the outside of the boiler. These consist of a flexible hose with two separate valves. One valve controls the water flow, and the second valve prevents any water from the system from returning to and contaminating the mains supply.

Internal filling loops, as the name suggests, are found inside the boiler. These are also known as 'combi loops' as they are usually seen in combi boilers. These have a slightly more-complicated structure than external loops but they work in essentially the same way.

To meet the relevant regulations, a filling loop must consist of a removable flexible hose, two isolating ball valves, and a backflow prevention device. A 4 bar pressure gauge is often included, although this is optional rather than compulsory.

Here at Heating and Plumbing World, we stock several boiler filling loops including products from manufacturers such as Altecnic Ltd and Pro-Line. This includes loops both with and without pressure gauges. Both of these are WRAS approved.

If you need further advice, please feel free to contact our team, who will be glad to help.