There are two basic hot water systems, an indirect, with all hot tap supplied from hot water storage cylinder, the direct, were cold water is heated on demand. The latter is the normal when all the cold water supplies come direct from the rising main. Clerkenwell Plumbers know systems.Instantaneous Hot Water Systems.Single-point water heaters may be heated by gas or electricity and are usually cited next to the point they serve. In the case of electric heaters, such as an electric shower, they must be wired to the mains through an isolating switch. An example is a combination boiler which is a central heating boiler and an instantaneous multipoint water heater.Indirect Systems.An indirect system has two tanks in the loft. The smaller one, has a vent pipe over the top and this is called a header tank or feed and expansion tank. It keeps the primary circuit full. This tank allows for the expansion of the water in the header tank as it heats up.Primary Circuit.With an indirect water system, the hot water cylinder contains a coil of pipe, which forms part of a run of pipework from the boiler. This is heated directly by the boiler and then indirectly heats the water in the cylinder through convection.Secondary Circuit.Water in the hot water cylinder is supplied from the cold water cistern, which keeps the cylinder completely topped up as hot water is used.Unvented (sealed) Hot Water Systems.This system is the same as an indirect system, except that it is connected to the mains and provide mains water pressure to hot taps and showers.Direct Systems.The water is heated to directly by circulation through the boiler. Water comes from the cold-water cistern into the bottom of the cylinder and then to the boiler. The boiler then discharges hot water currently in the top of the cylinder and forces the colder denser water at the bottom through the return pipe back to the boiler. A Clerkenwell Plumber is skilled.Immersion Heater.Another form of direct heating, using one or two electric immersion heaters, with around 1kW of heat required for every 45ltr of water. This is rarely the sole form of water heating in the home these days and is usually used to supplement the boiler system in summer.