What is an AGL (anti-gravity loop) and when do I need one?

The AGL (anti-gravity loop) is a U-bend in the hot pipe supply created by dropping the pipe down 400mm before rising up again. The AGL prevents air in the system tracking up into the pump chamber and prevents back siphoning of water away from the pump which can cause aeration issues.

If the pump is above the dome of the hot water cylinder, we would advise using a side entry No-Stop Essex flange and AGL.