What's the best type of boiler? Conventional, system and combi boilers compared

Need a new boiler but not sure which one is best for your home? We compare the costs, savings, energy efficiency and general pros and cons of conventional, system and combi boilers.

When should you buy a new boiler?

The annual energy price cap has more than doubled since last summer, meaning the penalty of having an old, inefficient boiler has risen dramatically as well.

So, when should you look to buy a new boiler?

In short, you may want to replace your existing model if it is more than 15 years old, you are continually paying to have it repaired, it is not producing enough hot water or it is in an inconvenient position.

Obviously, getting a new boiler isn't cheap: heating specialists Heatable.co.uk estimate it'll cost anywhere between £600 and £2,000 depending on the model and system required.

However, given the sky-high energy bills, that new boiler will soon pay for itself and save you a fortune in the long term.

Consider the following: Heatinghub.co.uk estimates that replacing an old boiler will generally cut your energy bills by between 14 and 34%.  

On a typical annual energy bill of £2,500, that means you could save more than £800 in the next 12 months alone - and the savings will be even greater if your energy bills are above average.

So your boiler will likely have paid for itself within three years. 

For those who feel the time is right to replace theirs, let's run through the different types of boilers, advantages and disadvantages, what costs you should expect, as well as tips on getting the best boiler for your needs.

Once you've decided on the best boiler for you, be sure to read our guide on how to save when buying and installing a new boiler.

Conventional boilers: costs, best models and more

Conventional boilers are the oldest type of gas boiler and is generally found in houses built in the 1950s and 60s. It has three parts – a tank, a cylinder and a boiler.

Tanks are usually found in the loft and, through a maze of pipework, they feed cold water to the boiler. They also require a hot water storage cylinder.

These boilers are normally only recommended if you have one already since the pipework is in place.

The advantage is they can meet high demand for hot water, for example, two people having a bath at the same time. But since the hot water is stored, once it is used up, you have to wait for more to heat up again.

They also take up a lot of space and because they require separate parts to be installed throughout your home, the process can be lengthy and costly.

A boiler may cost around £2,000 overall whilst a cylinder can set you back approximately £1,000, excluding installation.

Home-heating specialists Boiler Guide recommend the Baxi 400 Heat, Ideal Logic Max Heat and Vaillant ecoTEC plus Regular.

Combi boilers: costs, best models and more

System boilers are similar to conventional ones but are connected to the mains water supply meaning there is no need for a water tank.

These boilers still require a cylinder to heat water and are ideal for properties with high hot water demand.

Another benefit is higher water pressure since it is coming from the mains rather than a tank in the loft, which relies on gravity to send water down the pipes.

If your home has more than two bathrooms, then a system boiler will be well equipped to deal with multiple people in the shower or bath at the same time, but you will run out of hot water once the cylinder is empty.

You can expect to pay a similar price for a system boiler (when compared to conventional ones), but installation may be cheaper as they are easier to fit. You will need space for the hot water cylinder such as an airing cupboard or loft and they are ideal for a large family home.

Boiler Guide recommends the Baxi 800, Worcester Bosch Greenstar i and Viessmann Vitodens 200-W.

Cut your heating bills: tips for your radiator, thermostat, boiler & more

Combi boilers: costs, best models and more

Combi boilers are the most popular in the UK and are fitted as standard in new builds. They are a combination of a water heater and a central heating boiler all in one.

This means they have no cylinder and give hot water on demand making them ideal for homes with one bathroom and an en-suite.

The water is heated up as you use it with the disadvantage being that the water pressure can be weak if two people are showering at the same time.

These modern boilers are energy efficient meaning lower energy bills, plus their compact size makes them quick, easy and cheaper to install and they can be easily fitted into a cupboard or corner anywhere in the house.

Combi boilers cost between £500 and £2,000 depending on the model. Boiler Guide recommends Worcester Bosch Greenstar I, Ideal Logic+ and Glow-worm Energy.

Choosing the right boiler: size and output

Choosing the right size boiler in terms of outputs in kilowatts is an important step.

If the output rating is too low, it won't be able to heat your home properly or provide enough hot water. And if the output rating is too high, you could waste fuel and end up with high energy bills.

Important things to consider include the number of radiators and bedrooms in the property, as well as the number of bathrooms and how many people live there.

If you have had an extension or people have moved out of the house since your last boiler was installed, then you may need to consider changing the size of the boiler to meet your requirements.

Want to know how much a new boiler installation will set you back? Try this handy cost calculator (opens in new tab).

What to consider before installing a new boiler

When it comes to installation, make sure to use a Gas Safe engineer and ask to see their card when they arrive. Registered and approved engineers are listed on the Boiler Guide website.

Getting at least three quotes is sensible, so you can compare prices and gauge whether they are fair. If a price is too low, then this may be a red flag warning that you could encounter problems in the future.

Most heating engineers will have partnerships with boiler manufacturers or access to trade retailers so their price will include the boiler itself together with installation.

The average installation will cost between £500 and £1,000 depending on a variety of factors such as the time of year, location and boiler type.

If you're looking to buy a new boiler, you can get a bunch of free quotes from local engineers by clicking on the ad below. Please note that we may receive a small commission if you do decide to buy through Boiler Guide.

Find a great value boiler plan with 24/7 Home Rescue

Why an annual boiler service is vital

Each boiler will come with a different manufacturer warranty length and pricier boilers may have longer warranties. Some warranties may go up to 14 years.

Once the boiler is installed have it serviced every year to keep the warranty valid. A gas boiler service costs around £60 to £100.

As your boiler gets older, there is a higher risk of a gas leak or exposure to carbon monoxide so even beyond the warranty period, it’s recommended to have a yearly service by a Gas Safe engineer.

Also, check your home and contents insurance to see if this covers boiler repairs or replacement.

It’s worth considering boiler protection insurance once your warranty runs out if you are not already covered by home insurance.

Avoid huge repair bills: get a boiler care plan from £12 a month with YourRepair

*This article contains affiliate links, which means we may receive a commission on any sales of products or services we write about. This article was written completely independently.