Unvented Hot Water Heating Systems.

When an un-vented hot water system is installed both the hot and the cold water supplies within the dwelling, deliver water at the taps or shower outlet at mains water pressure. Cold water from the mains is delivered to the base of the cylinder, the water is heated, then when a tap or shower is turned on the mains water pressure pushes the hot water out.

To allow the water that is heated in the cylinder to expand as it is heated, an internal or external expansion vessel is used; a pressure relief valve is also fitted should the vessel fail.

An un-vented hot water storage cylinder can be heated directly via an immersion heater or indirectly by most heating systems providing it is not a solid fuel burning appliance They are ideal where high performance is required or in multi story properties where it would be difficult to gain the necessary head of water via a cold water storage tank to feed taps on the upper floors.

Since introduced to the UK, these systems have grown in popularity. An unvented hot water system doesn’t have a cold water tank and the sealed (unvented) hot water cylinder is instead fed directly from the cold water mains.

Unvented hot water systems can be dangerous so a number of safety features have been incorporated into their design, including: cylinder thermostats, expansion release valves, back flow pipes and air gaps to allow for expansion. Unvented cylinders come in a range of sizes and can be made of copper, stainless steel or low-carbon steel.


Strategically based in Bournemouth we offer a complete plumbing, heating service on the south coast, Dorset and Hampshire.

Emergency Service – We offer this service to domestic, industrial and commercial customers. Under normal operating conditions we can respond on the same day by calling our office on 01202 557 158



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