Filling loop on cylinder tank

Before you start

The heating should be turned off and should preferably be cool.

The filling loops for these types of systems are usually found in the airing cupboard and aren't part of the boiler at all. This is classed as a pressurised heat only system, as there is still a hot water storage cylinder in the property which stores the hot water. This type of system is sometimes linked to solar power as well.

Somewhere in the airing cupboard you should be able to see what looks like a flexible metal tube with two valves at either end. This loop can be used to top up the system pressure. As the loop is not likely to be anywhere near the system pressure gauge, which is probably on the boiler, it can be tricky to fill up to the correct level 1.5 bar. The example below shows the location of a filling loop (identified by the blue arrow) on this sort of system.

Let’s give it a go!

Slowly, open one valve at a time and allow a small amount of water into the system for maybe for 3 or 4 seconds. Close both valves and go to your boiler to check to the pressure gauge to see what the pressure reads. If the desired pressure has not been reached, repeat the process until you top up to 1.5 bar. A second person would be handy as they can keep an eye on the pressure gauge as you top it up. The picture below shows a typical location for a filling loop on a Baxi Megaflo system.

If you find that you’re regularly having to top up your system pressure (e.g., more than once every 2 or 3 months) it suggests there may be a leak somewhere on the heating system. There could also be an issue with your boiler. Please check all radiators, pipework, and valves to see if you can identify any leaks that may be causing this problem.