James Elston

James Elston

Published April 9, 2024

The average installation cost for a new combi boiler is between £1,500 and £4,500, including the boiler unit itself and the cost for installation. Installation alone ranges between £400 and £500. However, these figures will vary quite significantly depending on the type of installation, such as switching from an old combi to a new combi or changing from a system or regular boiler to a combi.

Combination boilers, or combi boilers for short, are popular boiler installations in UK homes. Why? Because they’re a central heating system and energy-efficient boiler in one compact unit! These sleek heating machines are space-savvy, supply on-demand hot water, and give you more bang for your buck – saving the environment and your wallet in one go!

But when trying to navigate the costs of installing the best new combi boiler for your home, things become a bit tricky. Right? Luckily, this is where our combi boiler installation guide comes in. 

Combi Boiler Installation Costs

Here is a breakdown of combi boiler installation costs depending on the scenario of the installation.

Scenario 1: Replacing a combi boiler

  • A new combi boiler costs anywhere between £1,500 and £3,500 – depending on the make and model.
  • The average installation cost is around £400 to £500 per day. However, two days for installation is the going rate.

Scenario 2: Replacing a system boiler with a combi boiler

  • Replacing system boilers with a new electric combi boiler (like Worcester Bosch combi boilers – Greenstar 2000 models) costs about £1,800 for boiler and installation.
  • These models offer a seven-year warranty when installed by professional gas fitters (10-year guarantee on the heat exchanger).
  • A new gas boiler replacement costs between £1,200 and £2,000 for the boiler unit itself and installations vary from £700 to £2,000.

Scenario 3: Changing from a regular boiler to a combi boiler

Scenario 4: Installing a new central heating system

  • Expect to pay roughly £3,500 to £7,000 to upgrade your central heating system.
  • House size, number of radiators, and hot water demands are the deciding factors when it comes to this final price tag.

How Combi Boiler Installation Works

Having a combi boiler installed is quick and easy. The installation process involves:

  1. Taking down the old boiler – obviously.
  2. Next, the filling loop is connected to the mains water supply pipe to fill and pressurise the central heating boiler.
  3. Oftentimes a magnetic filter is installed to stop corrosion (rust), sludge, and other debris from building up and clogging your heating system. It prevents this icky stuff from reaching the heat exchanger (the main component responsible for heat generation).
  4. All relevant pipework and boiler components are prepared, measured, and installed.
  5. The new boiler unit itself is then fitted.
  6. Flue and condensate (wastewater) pipes are checked or replaced to ensure a safe exit of waste gases.
  7. Combi boiler installation fitters will bleed radiators to release any trapped air in your new combi boiler and heating system. This ensures there are no blockages or obstructions that may affect water flow.
  8. Lastly, your central heating boiler system will be turned, repressurised, and voila – one happy homeowner! Sounds complicated, we know. So, read our guide on how long it takes to fit a new boiler to learn more about all the nitty-gritty details of the process.

Top tip: Take advantage of UK Government-backed heating schemes, like the Boiler Upgrade Scheme, to see if you qualify for free boiler replacements.

Advantages of installing a combi boiler

  • They are space-savvy heating solutions
  • Affordable and reliable boilers (especially when you opt for one of our recommended cheap combi boilers)
  • Provide instant heating and hot water
  • Green energy alternative (A-rated boilers)

Considerations for combi boiler installation

  • Home size, including the number of bathrooms
  • Number of people in the house
  • Lifestyle and habits
  • Hot water demand needs

When To Consider A New Combi Boiler

These eight boiler symptoms are telltale signs that your current boiler is on its last legs:

1. Leaks or drippy pipes: 

The most common cause of leaking boilers is damaged internal parts, like heat exchangers or faulty mechanisms, such as seals and valves. Check for leaks under the boiler unit itself or along any external pipe networks. If ignored, water leaks can be a potential safety hazard, causing anything from electrical short circuits to long-term water damage.

2. Little-to-no hot water

When heating and hot water are inconsistent (or non-existent!), it might be time for a boiler replacement. Usually, a lack of hot water means something is going on with the heat exchanger. This could also show up as cold spots on radiators or underfloor heating.

3. Loss of water pressure

Most boiler pressure readings should be between 1.5 and 2.5 bars. Sometimes, the pressure is easy to fix by simply topping it up with water. However, if your current boiler is consistently losing pressure – or showing error codes – for an extended period, it might be time for a new boiler installation.

4. Strange noises

Weird noises from your boiler, like gurgling, whistling or bubbling sounds, are not a good sign. This shows there’s something wrong with your boiler. First, call heating engineers for a full analysis of your system; they will be able to fix the problem or advise on a boiler replacement.

5. Odd smells

If you smell boiled eggs (without having one for breakfast) or notice the smell of gas from your boiler, it could mean your unit has a gas leak. This is serious business – shut off the gas supply immediately and call professionals for help.

6. Parts no longer available

If you have an old boiler at home, parts and spares can be an issue – which means you might have to replace your boiler after all.

7. Frequent breakdowns

Knowing the answer to “How old is my boiler?” is very important. If your current boiler is 15+ years old, it’s no surprise it will eventually start packing up. Boilers usually have a lifespan of 10-15 years, so once that milestone is reached, it’s probably time for a replacement.

8. Increased energy bills

If you notice higher-than-normal energy bills, for no logical reason, it means your boiler isn’t operating efficiently and is using too much fuel to generate heat. 

Are you wondering if a new boiler will save you money? Well, switching to an energy-efficient combi boiler can save up to £350 on your annual energy bill, according to The Energy Saving Trust!

Top tip: Are you asking yourself how often should a boiler be serviced? Regular services should be done at least once a year to keep your heating system in tip-top condition.


Can I install a combi boiler myself?

No, it is illegal to install a new combi boiler – or any new boiler, for that matter – by yourself. Unfortunately, there’s no DIY solution for this one, as registered and trained Gas Safe installation engineers need to do the job.

Where can I install a combi boiler?

The fantastic thing about combi boilers is their compact size. This makes kitchen cupboards, behind walls or in bathrooms the perfect installation site.

Is a combi boiler installation okay for a four-bedroom home?

This is a tricky one to answer. Combi boilers may be fine for four-bedroomed homes if your hot water demand is low. If not, you’ll find that even the best combi boiler will struggle to keep up with your hot water demands.

Does the size of a combi boiler affect the installation costs? 

Yes, the kW output or size of your combi boiler can affect the overall installation costs. Bigger boilers, such as 30 kW combi boilers or 40 kW combi boilers, may require adjusting your current pipework to handle the higher output. This is especially the case if you are switching from a small combi boiler to a larger model. 

However, if you are simply replacing your combi with a similar-sized, new combi, then the installation costs won’t necessarily be affected. 


So, there you have it – a complete combi boiler installation rundown! Ensure you have considered factors like house size and heating demands before having a new boiler installed.

Once these have been considered, you’re free to opt for an electric or gas boiler – whichever one is best suited to you and your home. Consider making use of UK Government heating schemes, like the Boiler Upgrade Scheme, as you may qualify for a free boiler replacement. Weigh up installation costs from different boiler installation companies, ask family and friends for recommendations, or speak to the Eco Happy team when deciding which is the best boiler installation for you.

James Elston

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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