Types of boilers explained

When it comes to boilers, knowing your options can save a lot of time and money.

An efficient boiler can make a big difference to your energy bills, but you could also reduce costs by switching to a different tariff. Enter your postcode below and see just how easily you can save hundreds of pounds a year.

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If you want to get the best out of your boiler, it’s important to choose one that fits in with your home and lifestyle. This guide will tell you everything you need to know about the main options, how they work and their advantages.

What's a condensing boiler?

Condensing isn’t actually a type of boiler, but a kind of boiler technology. Most modern boilers, regardless of their type, are condensing boilers – meaning they capture some of the escaping heat and re-use it. This makes the boiler much more efficient.

Conventional boilers

Also known as traditional or open vent boilers, these have both a cold water supply tank (usually installed in the loft) and a hot water storage cylinder. They best suit homes likely to need hot water in multiple places at once, such as larger houses with multiple bathrooms.


  • Since there’s always a ‘reservoir’ of hot water available, they can provide for more than one use at the same time


  • When the hot water runs out it can take a long time for it to be replaced
  • Having both a tank and a cylinder requires extra space
  • Installation can be more expensive because both a tank and a cylinder are needed

System boilers

Sometimes called ‘sealed system’ boilers, these have only a hot water cylinder. They take up less space than a conventional boiler, but still allow for multiple hot water uses at once.


  • You don’t have to find space for a cold water tank in the loft
  • You can get hot water from multiple sources at once


  • Hot water isn’t provided instantly and can run out
  • You still need to make space for a hot water cylinder

Combination boilers

Combination or ‘combi’ boilers don’t require either a water cylinder or tank – they supply hot water directly from the mains supply. Best for smaller or low-occupancy homes, combi boilers are particularly space and energy efficient.


  • No need to worry about planning ahead or running out of hot water
  • Since there’s no heat loss from a hot water tank, combi boilers are the most efficient type
  • Not having a water cylinder or tank saves space


  • As no water is stored, multiple uses are likely to cause low water pressure
  • Extended hot water uses, such as filling a bath, can take longer because the water is heated on demand

What to consider when choosing a boiler


New boilers can range in cost from about £500 to £2,500 depending on size, brand and type. Make sure you don’t forget about installation costs, too – system and conventional boilers can be more expensive to have fitted than combination ones because of the water cylinder and/or tank.


If reducing your energy bills and carbon footprint is a priority, make sure you consider how much heat your boiler is likely to lose. Modern condensing builders are often similar in efficiency level, but selecting the correct size and type of boiler for your needs is key to reducing waste.


Designate a space for your boiler before you buy it, factoring in any water cylinders or tanks that may need to be fitted in the loft. You also need to consider the amount of hot water your home will need at a time, which can differ wildly depending on things like number of bathrooms and occupants.


A cheap boiler can seem like a good idea, until you end up paying the difference in repair costs or finding your hot water gone in the middle of a shower. Some research into the most reputable and reliable brands can go a long way.

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