As a forward, the Energy Saving Trust have recommended hot water cylinders that are insulated at the factory before distribution, for more efficient hot water storage. The normal hot water systems fitted in British homes are usually these types: Vented hot water cylinder (with cold water tank in the loft). Unvented hot water cylinder (no cold water tank). Combi boiler with hot water on demand direct from boiler (no hot water  storage system). These systems are able to be helped with new eco-technologies like a Solar hot water system and the ground source heat pump. A Swiss Cottage Plumber can work on any system. The Vented Hot Water Cylinder System is a very common hot water system found in most homes and works on low pressure. It has a cold water storage tank fitted in the loft, with a copper hot water cylinder usually in an airing cupboard. The water in the cylinder comes from the header tank in the loft which is supplied from the mains. The cylinder water is heated either by an electric immersion heater (directly) and, or by a central heating boiler (indirectly). The hot water in the cylinder is used to supply the hot taps. The header tank is also an expansion tank, so as the water in the hot water cylinder heats, it expands and any excess returns to the header tank with a vent for trapped air to escape in case of pressure build up. Swiss Cottage Plumbers are professionals. Unvented Hot Water Cylinder System is a pressurised hot water cylinder that is fed straight from the cold water mains supply, supplying the hot water at cold water mains pressure to taps and showers. The mains cold water is fed into the bottom of the cylinder, and then heated, and so, if a tap or shower is operated, the hot water is supplied under the pressure of the mains. To allow the heated cylinder water to expand an expansion vessel is fitted and the system includes a pressure relief valve.