Combi boiler replacement & installation guide

Why should you replace your combi boiler?

You may benefit from getting a new appliance if your existing boiler is old and inefficient. New models are significantly more energy efficient than older designs. In fact, new condensing boilers are at least 25 per cent more efficient than non-condensing models, and new Viessmann condensing boilers can achieve efficiencies of up to 98 per cent. So, replacing your current appliance could help you to reduce your energy bills and lower your carbon footprint.

It’s also worthwhile considering combi boiler replacement if your current appliance is prone to breakdowns. As long as it is regularly serviced, a good quality new boiler should provide you with years of trouble-free use. Replacing an old, inefficient boiler with a new model can add value to your home too, which could be important if you are planning to sell your property in the future.

What is a combi boiler?

Combi boilers (short for combination boilers) are very popular in the UK. These appliances combine a high-efficiency water heater and a central heating boiler in a single compact unit. They provide hot water on demand and can be an efficient, space-saving solution in small to medium-sized properties.

Find out more about them here.
 

What are the benefits of a combi boiler?

There are many benefits of a combi boiler, including:

• Compact and space-saving designs, ideally suited to smaller properties
• Only one unit is needed for both heating and hot water
• No need for a separate pump, hot water cylinder or cold water storage tank
• Hot water is delivered to your taps and shower at mains pressure
• Greater reliability due to not constantly switching on and off, which means less wear and tear on components
   

What size combi boiler do I need?

When buying a replacement combi boiler, bigger is not necessarily better. Rather than looking to buy a boiler with the highest output, you should match the size of the boiler to the output of your home.

If you buy a boiler which is too small, you will find that you are not able to heat your home adequately or produce enough hot water. On the other hand, if you buy a boiler which is too big, you will find that you are producing more heat than required, which will increase your bills, waste energy and produce unnecessary emissions.

The sizing guide below will help ensure you buy the right size boiler for your home:

• 24-27 kW: small one to two bedroom house or flat, with up to 10 radiators and one bathroom
• 28-34 kW: medium three to four bedroom house, with up to 15 radiators and one to two bathrooms
• 35-42 kW: four or more bedroom large house, with up to 20 radiators and two or more bathrooms
   

What is a storage combi boiler?

A storage combi boiler combines the features of a system boiler and a combi boiler in one package, meaning it is equipped to provide efficient heating and hot water in large volumes.

With a storage combi boiler, there is no need for a separate domestic hot water (DHW) cylinder, so these appliances are easier to install than system boilers and they are an ideal solution for properties with limited space.

Storage combi boilers are perfect for households with a high demand for hot water.

Who can install a combi boiler?

By law, all gas boilers - including combi boilers - must be fitted by a Gas Safe registered engineer. The Gas Safe Register is the only official registration body of gas engineers and business in the UK. All engineers on the register are approved and qualified to work on gas appliances.

So, when searching for an engineer to install your new appliance, make sure they have this certification. It’s also a good idea to get a few quotes before you make a decision, and you may want to read some customer reviews for added peace of mind.
 

What can I expect during the installation?

Before your qualified heating engineer comes to your home to complete the installation, they will ask you certain questions to ensure they are prepared and equipped to complete the work. For instance, they will want to know where your existing appliance and the flue are located, and they will ask you how many bathrooms and radiators you have.

When they arrive to start the work, they should bring all the equipment and materials they need to finish the job safely and efficiently. Good engineers will also ensure that they cover your floors and surfaces to protect them and clean up thoroughly after themselves when the work is done.

Straightforward combi boiler installations can usually be completed within a day. However, more complex fittings can take longer. For example, your installation may take longer than a day if you need your heating system to be powerflushed or if you’re changing the location or type of boiler. Your engineer will be able to advise you on how long the fitting will take before they begin the installation.

After completing your combi boiler installation, your Gas Safe registered heating engineer will give you documentation proving the appliance complies with all the necessary building regulations. Ensure you keep this paperwork. They will also show you how the new heating controls work.
 

How much does combi boiler installation cost?

When you’re calculating the cost of replacing a combi boiler, it’s not only the price of the new appliance that you’ll need to bear in mind, but also the installation work. This cost varies depending on the particular Gas Safe registered engineer you choose and how complicated the installation is. For example, if your heating system requires a powerflush or you will need to have extra pipework fitted, you can expect to pay more than you would for a simple installation.

As a very approximate guide, the cost of fitting a combi boiler on a like-for-like basis could be around £600, while installing a combi in a new location could cost around £1,100.

It’s always useful to check a number of different installers to compare competitiveness, and make sure you get fixed price quotes so that you know exactly how much you’ll be expected to pay.

We hope this combi boiler installation guide been useful. If you have any further questions, please contact our friendly and helpful team.