The combi boiler, unlike the traditional boiler, takes its cold water supply directly from the mains water supply producing hot water on demand. Therefore, this type of boiler does not require a hot water cylinder in the airing cupboard or a cold water cistern and small header tank in the loft. All the major components of a combination boiler are housed in one unit, which makes them very convenient to the installer, and they are often fitted in the existing airing cupboard, replacing the hot water tank. Combi boilers are especially suitable for smaller households although the latest models seem more capable than their predecessors.
A combi boiler heats water on demand for taps and showers. Consequently the water flow is determined by the temperature required, but is not limited by tank size. This high pressure/low flow can mean that a bath takes longer to fill but is perfect for showers and dispenses with the need for shower pumps which might be necessary in a conventional system with a low pressure head. However, since the system is fed directly from the main, flushing a toilet may lead to the hot water temperature fluctuating.
An immersion heater cannot be used alongside a combination boiler system as there is no cylinder for it to be fitted to.
In the UK the are several leading manufactures of boilers, some of the more popular boiler companies are Potterton Boilers and Worcester Boilers. Both Potterton and Worcester make combination boilers for a variety of situations.
Since all taps, showers, toilets are fed with mains pressure, in old installations there may be a need to change tap washers, change wc ballcocks to high pressure ones, or fit high pressure thermostatic controls to showers.
The combi boiler, or combination boiler, is part of a pressurised system and will require occasional re-balancing. For example, when you bleed a central heating radiator and the combi boiler shuts down because the pressure is too low.
As with all boilers, regular gas safety checks and regular servicing should maximise boiler efficiency and minimise boiler breakdowns.
Potterton boilers and Worcester Boiler help and advice, including central heating systems can be found from Red Q Design
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