Complete guide to a new combi boiler installation

Combination boilers or “combi” boilers are one of the most popular choices of home boiler systems within the UK. True to their name sake, these heating systems combine efficient water heating with powerful central heating in one to provide households with on demand hot water and heat.

Our A-rated gas combi boilers are a great choice for most homes. They’re typically easy to install, compact, and available in a range of sizes and outputs.

Try our free quote service today if you’re interested in getting a new combi boiler installation or if you’re facing any trouble with the one you have installed. Our sales team will be in touch in a jiffy.

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What is a combi boiler?

A gas combi boiler is designed to be a highly-efficient means of heating the water within your home at the same time as providing central heating. Combination boilers control your whole central heating system directly from one, compact unit and provide a range of advantages based on factors such as space, energy and costs.

How does a combi boiler work?

One of the main features of combi boilers is their ability to provide instantaneous hot water without water tanks or cylinders, making them typically easy to install and less likely to take up excessive space.

This water is filtered through your pipes and fed into your household taps, whilst also being used to heat up your radiators. By turning on the hot water tap, you send a signal to the combi boiler to start heating water from the inside of the system.

Once heated up by burning gas inside of the boiler, the heat exchanger transfers the majority of the heat to the cold water. This hot water is then delivered to the taps, as required.

Are combi boilers the same as condensing boilers?

Modern combination boilers are manufactured to double as condensing boilers This means combi boilers are able to generate water vapour condensation to extract additional heat from its fuel. This is designed to make combi boilers even more energy-efficient, as they produce more heat with less energy. That could potentially enable you to reduce your monthly bills.

The control valves in combination boilers operate in different directions. This allows your combi boiler to either allow water to flow through the central heating system, or divert it to the appropriate hot water tap—but never both at the same time.

Combi boilers also give you the option of pre-setting your desired room temperature. This programmes the boiler to work with the room thermostat to ensure your home is heated as you like.


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What are the advantages and benefits of a new combi boiler?

More and more homeowners are deciding to replace their conventional boiler with a combi boiler, which are typically more efficient. This isn’t surprising when you consider the multitude of advantages that could come with installing a new combi boiler into your home. Buying a combination boiler could positively impact your finances, the decor of your home and your overall lifestyle.



There’s no need for any separate tanks or cylinders with combination boilers.

Combi boilers have everything you need packaged in one, leaving you with plenty of room to decorate your home as you please. Especially if you have limited space.

Instantaneous Hot Water

By installing a combi boiler, you provide your household with on demand hot water.
No water tank = no waiting time for your hot water!

Efficient & Economical

Combination boilers are designed to be highly-efficient, producing condensation in order for more energy to be used rather than wasted.

They also only heat the water you use, enabling you to potentially make huge savings on your energy bill. You could save up to £840!*1


The cold water released from a combi boiler is more likely to be safe for you and your family to drink. This is because it is fed directly from the mains. However, please note this is subject to environmental water advice in your area.

This is not always the case with conventional boiler systems as they tend to store cold water in tanks.


As combi boilers release water directly from the mains, they are less likely to accumulate sludge or debris.

This may help prevent boiler issues such as kettling from occurring and could thus save you money in future repair costs.

Potentially capable of boosting your home’s appeal

Due to the numerous advantages of having a combi boiler, it's definitely a value-add for your home.

You could even add it to your list of selling points if you ever choose to sell your home.

We aim to only install products supplied by the best boiler brands, to ensure your home heating is functioning in the best way, at all times. Here are some examples of popular brands that manufacture gas combi boilers:

Worcester Bosch

Worcester Bosch Logo

A popular choice for UK homeowners. Worcester Bosch provides premium quality, environmentally-conscious combi boilers.

Their boilers have been rated Best Buy by a Which? Online review.

Learn more about Worcester Bosch boilers


Ideal Logo

Based in Hull, Ideal values customer service and innovation.

Their boilers have been recommended by Good Housekeeping Readers, and have a 4-star Which? Online review customer rating.

Learn more about Ideal boilers


Vaillant Logo

Established in 1874, this brand pioneered the combi boiler over 35 years ago.

They have continued to create premium heating products ever since.

Learn more about Vaillant boilers

Most popular gas combi boilers

Selecting a boiler for your household can be a difficult decision to make. If, like many homeowners, you’re struggling to make a choice, here’s an insight into our top 4 selling boilers for 2021:

1. Worcester Bosch 4000 25kW

  • Combination boiler, natural gas
  • Suitable for small to medium households
  • Sleek modern design - with digital display
  • Instantaneous hot water

Read our review
2. Worcester Bosch 4000 30kW

  • Combination boiler, natural gas
  • Suitable for small to medium households
  • Modern design with easy to use digital, colour display
  • Operates well in low water pressure areas
  • 'Quick tap' water saving function helps reduce water waste

View spec and reviews
3. Ideal Logic 24kW

  • Combination boiler, natural gas
  • Designed with a backlit display & user-friendly controls
  • Designed with an easy to use pressure gauge
  • A suitable choice for most smaller properties with one bathroom
  • 395mm x 700mm x 278mm (Width x Height x Depth)

View spec and reviews
4. Ideal Logic 30kW

  • Combination Boiler, natural gas
  • Compact design
  • Designed with easy to use controls
  • 395mm x 700mm x 278mm (Width x Height x Depth)
  • An ideal choice for most households with limited space and no more than one bathroom

View spec and reviews
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How much is a combi boiler and how much does it cost to install?

“How much will a new combi boiler installation cost?” is a question on the minds of a great deal of homeowners in the UK. New combi boiler prices are dependent on a number of factors. These can include the type of boiler it is, its size, and the complexity of the installation process.

Are combi boilers expensive?

Often the cost of the combi boiler itself will be significantly lower than the overall price given by the person installing it. This will usually be due to the additional cost of installation, which can indeed be a complex process. Although this overall cost may seem expensive, it is important to remember that you are paying for quality. All installations should be carried out by a Gas Safe registered engineer who will follow strict protocol checks and procedures. This should provide you with peace of mind and allow you to have confidence in the fact that your installation has been completed to the highest regulated standard.

At HomeServe, we seek to offer customers access to flexible ways to pay for their new boiler installation. If you’d like to find out about the finance options that could be available, visit our access to finance page*2.

Boiler prices can also be affected by the product’s brand. Here at HomeServe, we aim to only install boilers of high quality from reputable boiler brands. This allows our customers to rest assured that getting their home heating up and running effectively is our priority.

How HomeServe can help you find a cost-effective combi boiler

To help this process, we provide our customers with a means of assessing how much it would cost to install a new boiler into their home. Our free quote estimate will take into account factors such as your current central heating system, how many radiators you have and any other additional requirements for your home heating system.

If you’d like to receive a indicative estimate of how much your new combi boiler installation could cost, try our instant, online estimate quote now which will also highlight any of our available combi boiler deals.


Which combi boiler is best for my home?

Gas combi boilers come in a range of shapes and sizes, each suitable for specific kinds of properties and rooms. Due to this, choosing the right boiler for your home can seem daunting. Nevertheless, ensuring you make the right decision for your home is important. After all, it can affect the quality of heating you and your family receive, and thus impact the level of comfort that you feel in your home.

A key factor to consider when making a decision about a suitable combi boiler for your home is the kW output required. kW outputs relate to the size of the boiler and are reliant on the number of bathrooms and radiators present within your household. The higher the kW output of your boiler, the better the supply of hot water you’d receive. However, this is not to say that you should purchase the highest output available-you must ensure that the boiler size correlates with the size of your home.

What boiler kW output do I need for my home?

Here’s a simplified guide to the average kW output needed based upon the property size:

24-27kW 1-2 bedroom, 10 radiators, 1 bathroom
28-34kW 3-4 bedroom, 15 radiators, 1-2 bathroom
35-42kW 4+ bedroom, 20 radiators, 2+ bathroom


(This information has been supplied by HomeServe UK limited and has been produced for information purposes only and should not be used or relied upon as a substitute for professional advice by a suitably qualified engineer.)


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* HomeServe Membership Limited brings you this discount offer from Help Link UK Ltd. The discount is only available to existing HomeServe Membership Limited policyholders. Only one discount available per boiler installation on all gas boilers. £500 discount is available on system swaps only i.e. conventional to combi. Customers who purchase a like for like boiler replacement (combi to combi or conventional to conventional) will be eligible for a £200 discount. The discount will only be applied to the cost of the boiler requested. Installation must be booked within 30 days from the point the boiler quote is accepted. No cash alternative will be given for the customer discount. The offer remains valid with the quote.

*1 Based on September 2022 Energy Savings Trust research on the average saving found in a detached house in England, Scotland and Wales when replacing an old gas boiler with a new A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator controls.

*2 Subject to application, financial circumstances and borrowing history. Terms & Conditions apply. Other options are available. Finance can be taken out with or without deposit and capital payments can be made at any time to reduce your loan.

About the lender

HomeServe Membership Limited is a credit broker, not a lender. Barclays Partner Finance acts as the lender. If you choose a credit option, Help-Link UK Limited trading as HomeServe may receive commission from Barclays Partner finance which is a fixed percentage of the total loan amount. For more information, contact Help-Link UK Limited.

Barclays Partner Finance is a trading name of Clydesdale Financial Services Limited, a member of the Barclays group. Clydesdale Financial Services Limited is authorised and regulated by the Financial Conduct Authority. Financial Services Register number 311753. Registered in England under company number 2901725. Registered office: 1 Churchill Place, London, E14 5HP.