How to Recharge a Depleted Air Gap in an Unvented Cylinder

Cylinders with Air Gaps have a volume of air in the top of the cylinder which is designed to take the expansion of the water when heat is added. If the Air Gap reduces then leaks can occur from safety relief valves. This does not automatically mean there is a fault within the system it may just need the Air Gap reinstating. The procedure to reinstate the Air Gap is very simple, please follow the guidelines below: 

1: Turn off the mains supply to the Unvented Cylinder

2: Open the nearest Hot tap to the Unvented Cylinder

3: Hold open the Temperature and Pressure Relief Valve on the Cylinder to discharge water via the Tundish, when the gurgling noise has stopped and no more water is flowing through the Tundish close the Temperature & Pressure Relief Valve

4: Ensure the Temperature & Pressure Relief Valve is closed, close the hot tap and turn back on the mains to the Unvented Cylinder. At this point the Air Gap will reinstate itself as the system fills

Note:

If you have completed the above and water is still passing from the Safety Relief Valve then you may have an issue with the Safety Relief Valve, contact a competent plumber to investigate. (If a Relief Valve is dripping for a long period of time wiring can form in the brass and a small amount of the seat will erode and not seal).