DIY Projects - Open vented system

The open vented system is fed from a feed and expansion tank located in the loft, which keeps the system topped up and also allows the water to expand as it heats up. There is also a vent line that releases any air in the system and returns any water or steam to the top of the expansion tank, in the event of the system overheating.

Some installations allow gravity to circulate the hot water up and through the coil in the storage cylinder, but most new installations use a pump to circulate the hot water up and through the coil in the storage cylinder.

Open Vented System with Gravity Fed Hot Water

1. Boiler 2. Storage cylinder 3. Feed and expansion tank 4. Cold water head tank 5. Central Heating Pump

Open Vented System Fully Pumped

1. Boiler 2. Storage cylinder 3. Feed and expansion tank 4. Cold water head tank 5. Central Heating Pump 6. By-pass valve