Boiler installation, Boilers, Combi boiler, DIY, Guides

How to Install a Combi Boiler on Your Own – DIY Combi Boiler Installation


What is a combination boiler??

A combi (or combination) boilers are a boiler in which gas is used for both the high-efficiency domestic water heater and central heating boiler within one compact unit. A combi boiler is an ingenious space-saving idea and an increasingly popular choice in UK homes. They are easy to install, simple to use, and economical to run. Installing a combi boiler might be a one-time hassle. However, your boiler still needs to be serviced now and then, especially if you are experiencing strange noises or temperature fluctuations.

How does a combi boiler work?

The conventional arrangement is to have a normal boiler that heats the radiator through a sealed water circuit. The storage cylinder has a hot coil in it to heat the water through which the radiator water flows.  A combi boiler heats the water only when a hot tap or shower is turned on.  This ensures maximum efficiency of the boiler. The hot water is delivered to the taps with pressure so that you can enjoy your shower.

What types of combination boiler are available?

Instantaneous: This used to be the most widely used combination boiler type and directly heats incoming mains cold water to supply your taps and all other hot water points.

Instantaneous condensing: Operates as an instantaneous boiler but saves more energy and has better and higher efficiencies than the standard combination boiler; this is the most commonly installed type now. In fact, exceptional circumstances aside, all new gas and oil central heating boilers fitted in the UK must now be condensing boilers by law.

Storage: This is an alternative to the Instantaneous combination boiler type mentioned above and is designed to give you better performance through the internal storage of heated water. The stored water can also give you an improved initial water supply from cold water mains when turning on the tap. Once the stored heat has been used, this boiler will tend to operate as an instantaneous type.

Storage condensing: Operates in principle as a storage type but at higher efficiencies.

Combined Primary Storage Unit: This is a special category of storage combination that will incorporate a huge water store allowing a high water flow rate to taps and other draw-off points and quickly heat radiators before the water store is used.

Why install a Combi Boiler?

  • A combi heater incorporates hot water being conveyed through your taps or shower at mains pressure.
  • Combi boilers are available in gas, electricity, or oil, depending on your fuel preference. Your combi boiler doubles as a central heating unit by adding a radiator.
  • The combi boiler doesn’t require a bulky storage cylinder and can easily fit into most kitchens or storage cupboards, making them the ideal system for houses with limited space.
  • Combi boilers are reliable. They are manufactured using proven technology.
  • Combi boilers are convenient and easy to use.
  • Another combi boiler benefit is that it can generally save you money on installation time and costs. No tank in the roof space means less pipework and a shorter installation time.
  • Unlike the conventional boiler, combi boilers provide on-demand heating to your radiators and domestic hot water.
  • Combination boilers are also versatile because they take care of your central heating as well as your hot water supplies.
  • It is economical and practical. These high-efficiency boilers reduce your energy bills.
  • Installing a combi boiler can be a bit difficult because the system gets added to your water mains, but they are much more likely to fit into your home because of their smaller size. The installation can also be more costly than system boilers connected to an old boiler system.

When do you need to install a new one?

new combi boiler installationBoilers can last up to 15 years, and if your boiler is reaching that age, then it’s time to get a new one. To ensure the best lifespan, annual services and maintenance are mandatory. But the older they get, the risk of malfunctions increases, especially if the initial installation was not done correctly.

Purchasing a new combi boiler is one thing, but installing it is a whole different story. While you can always hire someone to perform the new combi boiler installation for you, taking the DIY approach can save you quite a bit of money. But before you actually dive in and start installing, there are different factors that you’ll need to consider.

The first is that combi boilers are relatively compact, so they’re perfect for smaller spaces. But this can also make the installation aspect of it a bit trickier too. Second, you will need to consider whether or not you want to purchase a fitter separate from the manufacturer or simply purchase it as an “all-in-one” option. If you aren’t sure how to install a combi boiler, then it might be wise to invest in a secure installation company because you could damage your newly bought combi boiler. If you absolutely have your heart on installing the boiler yourself, you need to do proper research on the correct installation techniques.

Most common combination boilers problems

  • Faulty automatic air vent.
  • The buildup of limescale in central heating pipes can lead to blockages and causes fluctuation in temperatures of hot water taps.
  • Faulty or blocked pressure relief valve. This may cause dripping from pipes.
  • Pump failure leaves you with no heating or hot water.
  • Faulty diverter valves may get stuck on hot water or central heating.
  • Rust causes leakage in water pipes and results in the loss of water pressure.

These are the problems or common malfunctions faced in combi boilers, but these can be easily overcome by regular maintenance.

The fitting of a boiler can be tricky, and faulty boiler installations are one of the most common malfunctions in DIY systems.

Can I install a combi boiler myself?

While installing a combi boiler on your own can be a challenge if you’ve never done it before, the truth is that just like anything else, which can also learn boiler installations with enough persistence. Plus, it will save you tons of money on installation costs. Some people like to avoid the hassle altogether and hire a combi boiler fitter to get the job done. But if you’re not one of these people, keep reading to learn the actual steps for installing your combi boiler.

If you want the most secure information on how to install a boiler, then you should consult with the supplying company and get the best and most modern installation instructions that will make your installation process a breeze.

Combi boiler installation steps

Installing a boiler on your water mains is no simple task, and you should take careful consideration before you attempt it yourself.

Let’s take a look at the steps involved with installing a combi boiler:

Read the instruction manual

  • First, read the instruction manual completely.
  • Study the installation diagrams will give you a good idea about how the system should look after it has been installed.
  • Layout all of the materials that you’ll need to work with and familiarise yourself with all of them.
  • Make sure that you have all the required components in place and understand what each one does before using it. 

Figure out where everything goes.

  • Figure out where everything is going to be placed about everything else.
  • Decide about the exact position of your new radiator.
  • Make sure that these elements have plenty of space around them.
  • You will also need all the relevant sealants to ensure that there is no leakage inside your walls that could end up damaging your property.

Know the pipe routes

  • When installing new radiators, you need to learn about the pipe routes in your home.
  • This will ensure that the combi boiler gets installed the right way with minimal issues.
  • Knowing the pipe routes also ensures that the combi boiler installation benefits both the bathroom and kitchen.

Fit the boiler into the wall

  • This is probably one of the more time-consuming aspects of the installation, mainly because you want to ensure it’s done right!
  • Take extra caution to ensure that the fittings are secured, and don’t forget to turn off all of the electrics and water before taking this important step.

Get your radiator installed.

  • If you want to heat your home effectively, you must choose the most appropriate radiators for your property.
  • All radiators are compatible with combi boilers.
  • A wide range of radiators will help you heat up from the smallest to the largest of rooms.
  • Large open plan kitchens and living rooms might require an additional radiator to provide effective heat.

Provide ventilation

A new radiator will require a small amount of air ventilation once you have successfully installed everything. To do this, you should :

  • Bleed each valve by turning the key or valve located at the bottom.
  • Do this until a small number of water spills over the top of the unit.

As you can see, installing a combi boiler isn’t exceptionally difficult. By following the tips in this article, you should be able to have it installed in a relatively short amount of time and with a minimal amount of hassle. The most difficult part about this type of installation is figuring out the combi boiler pipework, especially if your home’s pipework is built into the walls.

How to find a professional boiler fitter

Even though the cost of combi boiler fitting can be high and it might be tempting to take a DIY approach, hiring a Gas Safe combi boiler installer to handle the job is always a safer option. The best way to save money is by requesting at least 3 quotes from trusted heating engineers. At Homeadviceguide, we can help you save time and money by getting you in touch with combi boiler fitters to help you with your combi boiler replacement project.

View the video below to understand better things you need to consider before you attempt to install a combi boiler. We think it is quite useful. 


What is a combi boiler –

Boiler Types: Which is the best boiler for your home –

Condensing boiler –

Jason R. Funk. “Boiler Basics” (PDF). Hughes Machinery. pp. 50–51. –

The new boiler that’s causing a heated row –

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