A closed system have a pressurised Expansion Vessel and Filling Point with a suitable pressurised cold water supply, By Pass Valve and a Pressure Relieve Valve. Normally, the cold water supply is taken from the house cold mains supply via a no return valve. The filling point is connected to the cold water supply by a filling loop, while filling and must be removed after filling to the required pressure. Most Combination Boiler systems are fitted as closed systems.
When the main circuit is closed or restricted, the by pass or the bypass valve will ensure water still to circulate through the heat exchanger, preventing the boiler from over heating with water.
If there is a by-pass-valve the pump’s pressure will open the by-pass-valve and provide flow through the heat exchanger.
The
vessel has a flexible neopren (synthetic rubber) diaphragm inside separating the
water and Nitrogen. The nitrogen is pre charged at about 0.7 to 1 bar is on one
side of the vessel. When the water in the system is heated it will expand and
the diaphragm is forced out of shape into pressurized part of the vessel to
accommodate the increased volume of water.
