Also called ‘regular’ or ‘heat-only’ boilers, conventional boilers provide central heating and stored hot water and are very common in traditional heating systems throughout the UK. and are the ‘go-to’ choice for larger homes with a high demand for hot water. They enable your household to run hot water from several taps simultaneously without a significant drop in pressure. They are also a cost-effective solution if your property previously had an older heating and hot water system and existing pipework is still in place.
What is a heat-only gas boiler?
More space is needed for conventional boilers but, as they are most popular for larger properties, this is not usually a problem. Requiring three tanks, this system typically has:

A cold-water cistern to store cold water (typically in the loft)
A small feed and expansion cistern to maintain the water level of the heating system (usually next to the cold-water cistern)
An insulated cylinder to store hot water (most often located in an airing cupboard)

While conventional boilers offer many benefits, there are some downsides. They do tend to be more expensive to install and are also not quite as efficient as combi boilers as some heat is lost from the water in the storage cylinder. Also, once the hot water has run out, you will need to wait for it to heat up again before using the hot tap.
Should I replace my conventional boiler with a combi?