Automatic filling valves

An automatic filling valve connects the mains water supply to the closed heating circuit. When circuit pressure drops below the set value, for example after bleeding the radiators or a small water loss, it tops up water automatically and brings pressure back to the correct level.

It reduces the need for manual refilling but does not replace regular checks: if it tops up often, there is a leak that needs to be found. The models in this category, by Brassform and ICMA, have a built-in pressure gauge for an instant pressure reading.