If you're considering upgrading your heating system, a combi boiler might be the perfect solution. These compact units handle both water and central heating, freeing up space in your home. In this article, we'll cover the costs, installation process, and benefits of switching to a combi boiler in 2025. Get ready to discover why combi boilers are a popular choice for modern households.

What exactly is a combi boiler?

Combi boilers (combination boilers) are a compact and efficient heating system that have two main functions: heating your home's water and feeding the central heating system. Combi boilers have no need for a separate hot water storage tank - normally found in older homes - which can free up a significant amount of cupboard or storage space when upgrading from an older system.

Get an instant price on a new combi boiler, starting at just £1,495.

What is the cost of a combi boiler?

Upfront costs.

The main factors that govern the upfront cost of a combi boiler itself is the output capacity that is needed to feed your homes central heating system, depending on the size of the property and amount of rooms that need the heated water supply to the radiators. This can mean that the average cost of a boiler in the UK can vary from around £500 to £2,500 depending on your needs. Other than that, the brand and model can have an effect on price, though most boilers today are of a similar standard and usually have a warranty attached. With that, brands like Vaillant and Worcester Bosch tend to be at the higher end of the price range which often come with extended warranty options and higher energy efficiency ratings.

Installation costs.

All combi boilers need to be installed by a Gas Safe registered professional, and the complexity of the installation is a big factor in the cost of installation. Most fittings are straightforward, especially if it's a replacement of an older combi system, but some can be more complex i.e. moving the position of a boiler or replacing an older system entirely. So depending on the circumstances, the costs can vary by an average of around £500 to £1,500 for most installations. So you could pay the entire value of the boiler for installation alone depending on your needs.

Running costs.

Running a combi boiler is relatively low compared to older systems, as the water is heated on demand and the boiler sits in an idle state in between uses for heating or hot water. The boilers energy efficiency rating will give you more insight into the actual cost, but combi boiler systems are generally considered one of the most cost effective options available.

How does the installation process work?

1. Selecting the correct boiler.

First, we need to know what type of boiler you need, depending on your home, the number of bathrooms and your typical water usage. A professional can advise on this but the process is relatively simple.

2. The installation process.

As mentioned above, this is not something that can be done by yourself. A registered Gas Safe engineer is required to install, check and, most importantly, test and sign off the installation to verify its safety. You will find a lot of plumbers also work as gas engineers and are Gas Safe registered. Though finding a reliable and available tradesperson in a hurry can be a difficult task.

The installation usually follows this process:

• Preparation: If the engineer is replacing and old boiler that will be removed first, prior to any other preparation work needed such as replacing any piping or making more space for the new boiler.
• Installation: The new boiler will be installed and connected to the homes gas and water supply and central heating system.
• Testing: The engineer will run a series of tests on the boiler to make sure it is properly and safely installed and works as expected with your gas and water services.
• Sign off: The engineer will explain how to operate the new boiler and make sure you're happy with the work. They will also usually leave documentation such as instructions for use and warranty information for the new boiler, then a gas safety certificate is issued, which is normally marked on the boiler itself with the inspection/installation date to inform the engineer at the next maintenance or servicing visit of the last service interval.

How long does the installation take?

The complexity of the installation can have an effect on the timeframe, but if the combi boiler is just a replacement of an older or faulty one, the replacement can take only a few hours, certainly within a day in most cases.

Replacing older boiler systems, moving the position of the boiler or fitting a system to supply an extended property with more rooms, for example, could push the installation time into a number of days.

What happens after installation?

Cost savings.
Even if your new combi boiler is replacing a similar one, not an older storage system, there could still be a cost saving on energy as newer boilers can operate at a higher efficiency than older ones.

Maintenance and servicing.
It is recommended that your boiler is checked and tested regularly by a Gas Safe engineer to make sure it's safe and operating efficiently.
For landlords it is a legal requirement in the UK to have all gas appliances checked and tested every year by a registered Gas Safe engineer to verify the condition and safety.