Four types of hot water system...
There are more than four ways of providing hot water, but these are the most
1) Open-vented hot water cylinder
2) Combi boiler
3) Mains pressure unvented hot water cylinder
4) Thermal store
I'll expand on these shortly.... This page will eventually replace the Mains
hot water page in the 'Miscellaneous' box.
Open-vented Hot Water Cylinder:
This is the most common. It is the ordinary dome-topped copper hot water
cylinder most houses have in the airing cupboard. A simple store of hot water
that can be heated by a central heating boiler or an electric immersion heater.
When both are installed, the immersion heater is a useful backup method of
obtaining hot water if/when the central heating boiler has a fault or breakdown.
A central heating boiler with a complex internal arrangement that allows it to
directly heat the domestic tap water as it flows through the boiler. Primary
advantages are low installation cost and no space required for a hot water
cylinder. Numerous drawbacks though. Combis discussed in detail here.
Mains pressure unvented hot water cylinder:
These run at mains pressure instead of being fed from a tank in the loft. The
hot taps run as fast as the cold mains taps! Showers work brilliantly and baths
fill quickly. They are expensive, need to be installed by a specialist with the
correct qualifications, and can go wrong if not serviced regularly. Just like
everything else really.
An initial page on thermal stores here.