Boilers Types Explained - Combi, Regular & System

What type of boiler do I need - combi, regular or system? Read our handy guide to find out which is the right boiler type for your house.

We explain combi, regular and system boilers and consider the advantages and disadvantages of each. We also advise when the circumstances are right for a particular system and whether to stick with what you have or change systems, for example when to move from an open vented regular boiler to a combi boiler system. 

6 Top Tips for Selecting the Right Boiler Type

  1. On a tight budget - replace your existing boiler with the same type of boiler in the same location
  2. Need more space - put the new boiler in the loft and free up the airing cupboard or a kitchen cupboard
  3. Want low maintenance costs - install a combi boiler with a 10 year warranty/guarantee from the manfacturer
  4. Extending your property and adding bathrooms - consider a system boiler with unvented hot water tank (if the water pressure is good)
  5. If you and your family have lots of showers at the same time - consider a system boiler with unvented hot water tank (if your water pressure is good)
  6. If you have old radiators or pipework buried in screed - stick with an open vented regular boiler

Boiler Types

There are three main types of central heating and hot water system: combi boiler, heat only (regular) boiler (which includes back boilers) and system boiler. We explain how each system works:

What is a combi boiler?

A combination boiler (or “combi”) is a compact, single unit that generates all the heating and hot water needed for the household.

How does a combi boiler work?

A combination boiler heats water via an integral heat exchanger directly from the cold mains. It provides instantaneous hot water.

This is different from a traditional system which stores hot water in a tank in advance of use.

A combination boiler does not need a hot water cylinder or tanks in the loft. Everything is done through a single, usually wall-hung, unit.

Advantages of a combi boiler
  • Creates space when removing old hot water tanks
  • Lower maintenance costs -  the integral heating and hot water functions are covered by the boiler manufacturer's warranty/guarantee
  • No long wait times for hot water
Disadvantages of a combi boiler
  • They do not work well in properties with poor flow rates and/or poor incoming water pressure
  • Hot water flow rates are reduced when providing hot water to two or more outlets simultaneously, although this is really only a problem in houses with two or more showers.
What is a heat only (regular) boiler?

A regular boiler (sometimes referred to a traditional, conventional or heat-only boiler) only provides heating.

How does a regular boiler work

A regular boiler provides heating directly to the radiators and works with a hot water cylinder to provide hot water.

These are usually open-vented heating systems (they can be sealed), i.e. there is a Feed and Expansion tank in the loft.

Advantages of a regular boiler
  • Low replacement cost as regular boilers are the cheapest type of boiler to buy
  • Work well with old radiators. Older radiator systems that are put under the high water pressure delivered by system or combi boilers may leak.
Disadvantages of a regular boiler
  • Only the boiler is covered by the manufacturer's guarantee/warranty. This leaves lots of other components on the system (e.g. hot water tank, pumps and valves) that are subject to replacement and breakdown

What is a back boiler?

A back boiler is a type of regular boiler that is situated in a chimney breast with a gas fire on the front.

It is currently not possible to replace a back boiler in the same location. For those with an existing back boiler that would like to replace it with a new boiler then one of the other options must be selected.

What is a system boiler?

A system boiler has all the same components as a combination boiler without the integral hot water production. Like heat-only boilers it works with a hot water tank.

How does a system boiler work?

Like regular boilers, system boilers work with a hot water cylinder. Unlike regular boilers, the system is not open-vented, i.e. there are no tanks in the loft, and all of the components that would normally be outside a regular boiler (pumps, valves etc) are integrated into the boiler.

These are a modern version of the regular boiler and are often installed along side unvented hot water cylinders.

Advantages of a system boiler
  • Good for properties that have a high hot water demand, i.e. lots of showers, as the unvented tank can deliver good hot water flow rates to multiple outlets simultaneously
  • Good cover from manufacturer's warranty/guarantee as there more of system's components are integral to the boiler.
Disadvantages of a system boiler
  • Good hot water flow rates depends upon good incoming mains water pressure, if the pressure is poor then internal flow rates will be poor

Which is the best boiler for my property size?

1 bedroom flat, two bedroom house, three bedroom house, large properties...we help you find the best boiler for your property size with our other site tools:

Find out which is the best system for you. Call to book a free survey with our expert engineers: 01634 826143

Call to book a free survey with an engineer