Changing to a combi boiler – is it right for you?

changing to a combi boiler
Credit: Worcester Bosch

If you’re thinking about changing to a combi boiler, consider four main questions:

  • Is my household the right type for a combi?
  • Will a combi boiler be better than my current boiler?
  • Would it be a straightforward installation?
  • Is it affordable?

If you’re looking to install a new boiler then fill in your details in a form anywhere on this page.

One of our partner installers will get in touch with you with a competitive quote.

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Is my household the right type for a combi boiler?

The combi boiler is perfect if you:

  • Have a small to moderately sized apartment/house
  • Live on the gas grid
  • Don’t have a massive water demand
  • Live in an area with decent water pressure

What is a small to moderately sized house?

We would say anywhere from 1-4 bedrooms. This is the rough kW of combi boiler you’d look at depending on this size.

24-27kW1-2 bedroom, 10 radiators, 1 bathroom
28-34kW3-4 bedroom, 15 radiators, 1-2 bathroom
35-42kW4+ bedroom, 20 radiators, 2+ bathroom
Stats: Homeserve

Any household larger than this is unsuited to a combi boiler as the demand would be too great. 

The combi boiler is perfect for living in a flat, apartment or smaller household with only a few people.

The cold water to be heated is drawn from the mains.

The more water in demand at once in the house, the weaker the pressure. 

As a result, the combi is best in a household without a very large water demand.

If you have 5 or more bedrooms and your house is full of people, it might be worth considering a system boiler instead.

This way more people could use hot water without a drop in water pressure.

If you have poor water pressure in your area and need a lot of water, you probably shouldn’t consider a combi.

What’s more, if your house is connected to the mains gas grid, you can use gas to power your combi boiler, and gas combi boilers are the most efficient boilers you can get.

changing to a combi boiler - gas efficiency
Credit: Ovoenergy
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Will a combi boiler be better than an old boiler?

Modern combi boilers are generally A-rated in terms of energy efficiency.

If your current boiler is between D- and G-rated you could save potentially hundreds of pounds per year.

The below table shows your potential annual savings, adjusted for your property type:

Your current boilerIts energy efficiencyFlatMid-terrace propertyDetached one-storyDetached two-storySemi-detached two story
GLess than 70%£90-£95£160-£175£145-£155£285-£305£185-£200
F70% to 74%£60-£65£115-£120£100-£105£200-£210£130-£140
E74% to 78%£50-£55£90-£105£80-£90£160-£180£105-£120

You’ll also save even more money by moving to a new combi boiler from a system or conventional boiler as the water is heated only when you need it.

In other boiler types, water is heated and stored in tanks or cylinders.

A lot of the time, this water isn’t even used, so any energy used to heat it is wasted (and what’s more, if you do use up all your stored hot water you’ll have to wait for it to be heated again!)

Aside from the financial saving, you could also save a lot of space in your household.

This is a further advantage of not needing a storage tank or cylinder – or the pipes used to connect to those units!

So if you switch from a system or conventional boiler to a combi boiler you will instantly have more space in your home.

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Is it easy to install a combi boiler?

This is dependent on the current state and type of your current boiler.

Straight swap in the same location (combi-to-combi)

A straight swap is as straight forward as it gets.

There is minimal change needed and shouldn’t take any longer than a day or two.

Another type of boiler (regular, system) to combi

Replacing another type of boiler is a bit more complicated.

New gas connections may have to be made, the flue could be relocated and the system may need a powerflush, all of which could take up to 3 days.

Boiler relocation (installing a combi boiler in a different part of the house)

If you’re wanting the boiler to be relocated, this results in plenty of additional pipework and manual labour.

The whole process might take 3 to 4 days to complete.

Is a combi boiler expensive?

There are three aspects to consider:

  • The cost of the boiler itself
  • The installation costs
  • The type of boiler you’re switching from.
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Cost of the boiler

Average prices for boilers are around £1,000 for small and medium-sized properties.

Boilers suitable for larger properties average £1,370 in price.

Installation costs

Labour costs typically look as follows:

What you might see on your quotePrice range
Boiler installation cost£630-£780
Cost of moving pipes£190-£310
Mechanical flush before installation£440-£535

Type of boiler you’re switching from

Generally, your total average costs of the boiler and installation will look like below, adjusted for boiler type:

Brand new combi£1700-£25001-2 days
Regular boiler to combi£2200-£25002 days
System boiler to combi£2400-£30002-2.5 days 
Back boiler to combi £2000-£24502 days 

The range in prices is mainly dictated by the price of the combi boiler you’re switching to.

It’s also influenced by whether you’re changing the location of the boiler in your property.

If you want more information on any of the above, feel free to read up on our more in-depth article on new boiler installation here.

Alternatively, fill in a form anywhere on this page and one of our partner Gas Safe registered installation partners will get in touch with you shortly with a competitive quote.

We help you save up to 54% on the cost of buying and installing a new boiler through comparing quotes between trusted local installers – so let us do the shopping around for you!

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Archie Everard

Archie is a content writer at Homesage, who has enjoyed freelance writing before and after his time at Oxford Brookes. Obviously he loves boilers most of all, but also enjoys reading, football and going to the pub!