Tel: 0800 114 3634

If you’re thinking about changing your boiler, it’s important to know the different types and how they work. The type of boiler you buy will depend on your needs and budget. There are three main types of condensing boiler: combi-boilers, system and heat only boilers. We appriciate that buying a boiler can be complicated however choosing a boiler doesn’t need to be daunting with our quick guide. 

A combi boiler provides heat for your radiators and domestic hot water on demand.

The name comes from the fact it combines all the functions of a traditional boiler, hot water cylinder and cold water tank set-up. All the major parts are in one unit, which makes them convenient to install.

When you turn on a tap, water is drawn from the mains, heated in the boiler and comes straight out of your tap piping hot.

Pros:

  • Instant, unlimited hot water supply – no waiting for the hot water cylinder to refill.
  • An economical choice for smaller households with low hot water demands.
  • Smaller heating systems – combi boilers eliminate the need for a cold water tank, hot water cylinder and airing cupboard.
  • Drinkable water at all taps – it's supplied straight from the mains.
  • Combi boilers can produce between 9 and 18 litres of water a minute (when the cold water is heated up by 35°C).
  • You can run a powerful shower off the bath taps with a combi boiler.

Cons:

  • Combi boilers can provide maximum water pressure through only one tap at a time. They're not suitable for big homes where multiple sources of water might be used simultaneously.
  • Combi boilers can't heat hot water fast enough to supply a power shower and are slow to run a bath.

A system boiler works on the principle of stored hot water. Many of the major individual components of the heating and hot-water system are built into a system boiler. The system boiler removes the need for a feed and expansion cistern, but there is still a cold water tank (unless you have a pressurised hot water cylinder).

It is the ideal choice for the modern family home which needs every inch of space for storage and has a high demand for hot water.

Pros:

  • Because there is a large tank of stored hot water you can use several taps at once.
  • No need for a feed and expansion tank in the loft.
  • Can be used with pressurised cylinders, so you don't need a cold water tank in the loft either.
  • Suitable for larger houses with higher hot water demand.
  • Fewer heating system components outside of the boiler means that installation is quicker, neater, easier and more efficient.
  • The pump is included in the system boiler, resulting in a fast response and more economical running costs.

Cons:

  • Hot water cylinder-reliant hot water systems take up more space than a combi boiler system.
  • Unless a cylinder is very well insulated it usually loses heat into its surroundings, thereby wasting energy.
  • The amount of hot water you can use is limited by the size of your cylinder. For instance you might run a bath, then need to wait for the boiler to heat up the water in the cylinder again before you can run another.

Heat-only boilers are the heart of most old-fashioned heating systems. They provide heat for radiators directly and produce hot water which is stored in a separate hot water cylinder. The cold water is normally supplied by a cold water cistern, usually in the loft above the boiler (a gravity feed) and there is also a separate expansion cistern.

Pros

  • There's a large tank of stored hot water – you can use several taps at once.
  • Suitable for larger houses with higher hot water demand.
  • Easy to replace in old-fashioned heating systems without too many pipework changes.

Cons:

  • Heat-only hot water systems take up more space than a combi boiler system.
  • Unless a cylinder is very well insulated it usually loses heat into its surroundings, thereby wasting energy.
  • The amount of hot water you can use is limited by the size of your cylinder.
  • The pump for the heating and hot water systems is housed outside the boiler and takes up more space.