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Which new boiler to choose

Whether you’re renovating a home or your old boiler has finally given up, choosing a new boiler doesn’t have to be difficult when you’ve got all the information you need. Read on to find out how to choose your ideal boiler.

Using Ideal Boilers’ Boiler Selector Tool

We can help you to choose the right boiler online – simply work your way through our new boiler selector tool, where you input various facts about your home, and you’ll end up with recommendations based on the information you give us.

Remember to use data that’s future-proof when you choose your new boiler. For example, if you only have one bath now but you’re planning a second bathroom in the next year or two, choose two baths.

Replacing your old boiler

Do you have an existing boiler system in the home (i.e. you’re replacing a system rather than installing one in a new build)? If that’s the case, the cheaper option might be to install the same type, as you’ll probably be able to use the same pipework, tank(s) and electric wiring. However, it might not be the best option. The old system might not have been the optimum one for your home setup.

In an old home, for example, the chances are you’d have a loft tank, a hot water storage tank and a boiler, but that’s probably because that was the only option when the house was built. Combi boilers only started making an appearance in the 1970s. If you have a small family with one bath, an electric shower and central heating, a combi boiler will almost certainly be sufficient.

Conversely, if you currently have a combi boiler but you have a large family and multiple bathrooms that often get used simultaneously, the opposite is the case. You could find that a combi boiler, even one of the larger ones, might not be enough.

It’s easiest to move from a conventional to a system boiler, or a system to a combi, because you simply stop using the cold and/or hot water tanks. You can leave them in place or have them removed – it’s up to you.

If you’re upgrading from a combi to a system, you’ll need a hot water tank. If you’re upgrading to a conventional boiler setup, you’ll need a hot water tank and a cold water tank.

The three types of boiler

When you reach stage 5 of the new boiler selector tool, you’ll be faced with three options: combi, system and heat only. Let’s have a look at what they are.

Combi boilers

Combi boilers pump water around your central heating system and deliver hot tap water on demand. So when you turn on your bath tap or wash the dishes, the boiler fires up and instantly heats up mains water. 


  • Hot water on demand, 24/7

  • Efficient – you only heat the water you need

  • Less space required – the unit is all there is (no tanks), so ideal if you don’t have a loft

  • Easier and cheaper to install

  • Uses mains pressure, so it’s possible to run a shower from one Perfect for small families or single occupants


  • They can struggle to meet the high demands of a large family or large home

  • You can only have one tap or central heating running at a time. When you run a hot tap, the heating will temporarily shut down

  • Will not work if you have low mains water pressure

System boilers

A system boiler powers your central heating system and gives you hot water. Unlike a combi boiler, the system boiler requires a hot water tank that feeds your taps, showers etc. The tank is warmed by circulated hot water from the boiler, rather like your radiators. It cannot heat water fast enough to be used on-demand.


  • Better for a large house or family with multiple demands for hot water

  • You can use the hot water tank in an airing cupboard

  • Can be used in areas of low water pressure An immersion heater can be included in the hot water tank as a backup or to take advantage of cheap overnight electricity to heat the water


  • They can be inefficient, as you will often be heating water you don’t use (although a timer can help you to heat water only when you need it most)

  • Once the tank has run out of hot water, you have to wait for it to refill and warm up

  • You need to have space for the tank – not always an option in smaller buildings

Heat only boilers

Heat only boilers have several common names: conventional, traditional, regular or open vent. This was the standard type of boiler installed in most homes before the 1970s. Like the system boiler, it requires a hot water tank, which feeds the taps and shower. The water in the tank is heated by a separate water system that circulates through the boiler. But there’s also a cold water tank (or possibly two), usually in the loft, which supplies the boiler with water.


  • Same advantages as system boilers (see above)


  • Same drawbacks as system boilers (see above)

  • You need one or two extra tanks in the loft, taking up more space and adding to the cost of a new installation

Choosing your new boiler

The choices of boiler may look complicated at first, but your options will usually be narrowed down by your circumstances. Once the type of boiler has been chosen, the only factor remaining is which particular model you choose.

The biggest difference between each model is the volume of water they can heat up at the speed required.

If you’ve input all the facts and figures about your home correctly, and factored in any plans to add more hot taps or bathrooms in future, you should be given the best model for your needs by the selector tool.

If you’re really not sure about which boiler to choose, enter your postcode into the “Find an installer” box on the home page, and arrange for one of our approved expert fitters to visit your home and assess your needs.

Find my new boiler