Which boiler is best? Combi, system or heat only?

publication date: Nov 27, 2017
author/source: Guest article - Hassle Free Boilers

What sort of boiler should you choose?

At this time of year, staying warm is a priority, but what if the boiler’s on the blink?

Replacing a boiler is a big investment so you’ll want to get it right first time… but the choice can be baffling, so we’ve spoken to the experts at Hassle Free Boilers to cut through the confusion.

To help you decide which boiler is best for your household, Hassle Free Boilers have created this useful checklist: How to choose a boiler. You can use this, along with expert advice from a Gas Safe-registered plumber, to choose which system best meets your needs.

These are the three main types of boiler and your choice determines whether you need a water cylinder and cold water tank or not. It’s important to remember there is no ‘best’ system; it all depends on the size of your property and the needs of the household.

Combi (combination) boiler
So called because they heat both the water and the central heating, combi boilers have become more popular in recent years, accounting for more than half of sales of domestic boilers in the UK. They heat the water directly from the mains when the hot tap is turned on.


  • Instant hot water on tap, all the time

  • They only heat the water you use, when you use it, so are cost-effective and efficient

  • They provide water to your taps at mains pressure

  • Ideal for smaller properties, as they are compact and don’t need a hot water cylinder or water storage tank in the loft

  • Frees up loft space for conversion, if required

  • No water pipes required in the loft, reducing risk of frozen pipes


  • Slight delay in hot water as it is heated on demand

  • Takes longer to fill baths

  • Possible reduction in water pressure when more than one hot tap is running

  • No warmth from hot water cylinder in the airing cupboard

  • No stored hot water in the event of a boiler failure

  • Not always suitable for large homes with several showers

Heat boiler
These are traditional/conventional boilers and require a cold water storage tank in the loft, and a separate hot water cylinder.


  • Hot water stored in cylinder, so available when you need it

  • You may still have a limited supply of hot water available in the event of a boiler failure

  • Ideal for older radiator systems or if you have several bathrooms which are used at the same time

  • Suitable for areas of low water pressure

  • Compatible with solar heating systems, with a secondary coil


  • You have to wait for the hot water tank to fill and refill, so hot water isn’t constant

  • Need space for the hot water cylinder and cold water tank

  • May need a booster pump for powerful showers

  • Quantity of hot water is limited by the size of the tank

System boiler
These require a water cylinder to store the heated water but no tank in the loft.


  • Economical

  • Ideal if you have more than one bathroom

  • Can supply hot water to several taps/showers at the same time

  • No loft tank required, freeing up space and reducing risk of frozen pipes

  • Quick and easy to install, compared to traditional boilers

  • Compatible with solar panels


  • You have to wait for the hot water tank to fill and refill, so hot water isn’t constant

  • Need space for the hot water cylinder

You can find out more about installing a new boiler here.

Read why we work with Hassle Free Boilers.

How to choose a boiler - Hassle Free Boilers

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