Changing to a Combi Boiler: What to Expect and the Costs

If you have recently purchased a new house, your current boiler has failed, or your boiler is more than 12 years old, you should consider replacing it with a combi boiler. Combi boilers are wonderful because they give both space heating and water on demand, eliminating the need for a hot water tank.

The boiler is probably the most important appliance in your home, especially during the winter months. And, a boiler breakdown can be a nightmare that you want to avoid at all costs. The idea of not having hot water and heating in your home in the depths of winter can beterrifying for any homeowner. Now picture this along with the task of purchasing and installing a new boiler whilst .

However, before we go onto discussing the costs of the purchase and installation of a combi boiler, let’s take an in-depth look at what a combi boiler is, the benefits of using one and why you should consider changing to a combi boiler setup.

Is It Worth Changing to a Combi Boiler?

As a homeowner, you probably know that there are many different types of boilers; however, a combi boiler is a boiler that provides both hot water, as well as central heating, for your home.

If you’re planning to replace the conventional boiler in your home with a combi model, then it is important to evaluate whether the replacement is worth it.

A combi boiler is an excellent way to get rid of hot water cylinders, attic tanks or extra pipes. These boilers produce hot water instantly whenever you need it so you don’t need a boiler tank installed in your attic that helps to free up a lot of space, which is especially beneficial in small homes and apartments, where space is a luxury.

While a system conversion can be expensive, apart from the cost of boiler installation, you must consider the benefit it offers in terms of saving on heating bills in the long run.

However, some important things to consider are that if you live in a larger home where the demand for hot water is very high or you’re on a tight budget, then a combi boiler may not be the right option for your home.


Combi Boiler Replacement

If you have decided to replace your existing boiler with a combi boiler, you can do this anytime at all. However, the process of replacing the boiler can be quite disruptive and time consuming.

It is best to get the system changed when you’re refurbishing your home or changing the flooring, especially if you have a boiler or heating system with tanks.

This will not only help to avoid the upheaval in your home for laying pipes under the floor, especially if you have carpeting, but it will also help to reduce the costs by combining the work.

Why Change to a Combi Boiler?

If you have purchased a new home and the existing boiler is more than 12 years old or if it has broken down, then you may consider replacing it.

You must determine what type of heating system is currently in place and decide on what type of arrangement you want. This will have an impact on whether a combi boiler is the right option for your home or not.

Reasons to change to a combi boiler include:

  • Combi boilers are available in oil, gas or electricity depending on the availability and preference of fuel.
  • A combi boiler is a space-saving option and can fit into most storage cupboards or kitchen spaces.
  • These are quite reliable, easy to use and convenient.
  • They are cost efficient and save on both installation time and cost.
  • They provide hot water on demand, whenever you want it.
  • Combi boilers are versatile and can take care of both your hot water, as well as heating needs.
  • They are practical, economical and energy efficient, helping to reduce your energy bills.

The Benefits of Changing to a Combi Boiler

Combi boilers have become quite popular in homes in the UK in recent years because of the various benefits they offer including:

Efficiency and Reduced Running Costs

One of the main reasons why landlords and homeowners prefer to change to a combi boiler is because it is very energy efficient. As per the Energy Saving Trust, if you replace a boiler that is 12 to 15 years old with an A-rated condensing combi boiler you could see savings of up to 40% on your energy bills.

The boiler has several components that undergo thermal stress every day and over time, they get corroded, which can reduce the efficiency of a regular non-condensing boiler to anywhere from 70 to 50%.

This means that you could lose around £30-£50 for every £100 spent on energy bills. Combi boilers with an A-rating are more than 90% efficient and can help to save money. There are some premium combi boiler models available that offer 98% efficiency or even more.

Another benefit of the combi boiler is that these boilers can produce hot water whenever required and you don’t need to store the hot water, while the system boiler or conventional boiler stores hot water.

And, of course the water cools down whether you use it or not and the boiler fires up again to heat the water, which is a huge waste of energy and money.

Space Saving

As discussed earlier, a combi boiler is a heating system that combines the central heating unit and the water heating system into a single body, which handles the heating, as well as producing hot water without the need for 2 separate boilers.

There is no need for a separate water tank system, which frees up a lot of space in your home and is a huge advantage for smaller homes and apartments with limited space. The only space needed is for the boiler, which can easily fit into your utility room or a kitchen cupboard.

What Is Involved in Changing to a Combi Boiler?

The process of changing to a combi boiler involves,

  • Removing the hot water cylinder of the old boiler.
  • Removing the tank feeding cold water, which is usually installed in the loft.
  • Drilling a core hole for the flue.
  • Upgrading the gas runs according to the current standard.
  • Upgrading the heating controls.
  • Installing the magnetic filtration system and the limescale filter.
  • Installing the TRVs.

Changing to a Combi Boiler—Installation Steps

While installing a combi boiler is a difficult task and needs patience and some learning, doing it as a DIY job can save you plenty of money. So, if you decide that you want to install the combi boiler by yourself, here are the installation steps.

  • Disconnect the old boiler and water heater.
  • Gather all the materials required to install the combi boiler and read the instruction manual properly.
  • To the basement wall, mount plywood on which you can mount the combi boiler.
  • Run the plumbing, gas and electrical lines to the plywood panel.
  • Fix the mounting brackets to the panel and then hang the combi boiler on the brackets.
  • Make 2 holes that are 4” in diameter in the wall of your home for the air intake vent and the exhaust vent. The air intake vent should be above the snow line, while the exhaust vent should be 12” from the air intake vent and 12” from the window.
  • Create the air intake and exhaust vents using PVC pipes and run the pipes from the combi boiler to the external wall.
  • Connect the cold water and hot water lines to the combi boiler so that it can deliver hot water to your domestic water systems and the heating system of your home.
  • Connect the electrical line and gas line to the combi boiler.
  • Run a condensate line having a limestone neutralizer from the combi heater to the floor drain or sink drain and drain the excess condensation using a condensate pump.
  • To regulate hot water production, fix an outdoor temperature sensor on the north side of your home.
  • Turn on the combi boiler, which will start producing hot water immediately.

Is It Hard to Change to a Combi Boiler?

Depending on the current boiler system you have in your home, changing to a combi boiler can be quite difficult, as well as time consuming.

In case it is a gas boiler change, then you need new gas connections, which means that only Gas Safe registered engineers can do it. If a plumber or you, do it without the proper certification, then you can face a heavy penalty or even jail time.

However, if you’re changing a gas combi boiler with an electric one, then this is quite simple because the plumbing is the same and can be fitted to your new boiler. Since the electric boiler does not have a flue, it can be changed without any restrictions.

Changing to a Combi Boiler—The Cost

An important factor to consider when changing to a combi boiler is the cost. Typically, if you have a small to medium-size home and you decide to install a combi boiler, it can cost between £1,800 and £2,000.

However, if you’re planning to change from an existing boiler, then the cost will vary depending on the type of boiler you already have installed in your home.

Combi to New Combi—Swap

LocationChangeAverage CostTime To Install
SameCombi to Combi Swap£1600 – £23001 Day
NewCombi to Combi Swap£2200 to £26002 Day

If you have a combi boiler already installed in your home and want to replace it with a new one because the model is very old, is not working properly or is damaged and cannot be repaired, then it involves a direct swap without the need for any conversion or extra work.

The cost of the change will depend on the location where you want the boiler to be replaced.

If you want to swap a new combi boiler for an old model in the same location, then this will take a day’s work and cost between £1,700 and £2,200.

However, if the swap of the new combi boiler is in a new location, then it could take around 1.5 to 2 days to complete the job and cost between £2,200 and £2,500.

Regular, Conventional or Open Vent Boiler to New Combi Boiler—Conversion

ChangeAverage CostTime To Install
Remove Storage Cylinder, Attic Water Tanks + Replace Existing Boiler£2100 – £26002 – 3 Days

Conversion is required to change a regular, conventional or open vent boiler to a combi boiler. This involves the removal of the attic water tanks and DHW storage cylinder and replacing the existing boiler with a combi boiler. The conversion will take around two days to complete and will cost between £2,200 and £2,500.

Back Boiler to Combi Boiler—Conversion

ChangeAverage CostTime To Install
Remove + Decommission Back Boiler, Remove Water Cylinder + Tanks Install New Combi Boiler£2500 – £31002 – 3 Days

If you have a back boiler installed in your home and you want to change to a combi boiler, then this will involve the decommissioning of the back boiler. You can either let it remain in place or remove it and discard it.

The water cylinders, as well as the attic tanks also need to be removed and finally, the combi boiler must be installed. The entire conversion process will take around 2 to 2-1/2 days and will cost around £2,400 to £3,000.

System Boiler to Combi Boiler

ChangeAverage CostTime To Install
Remove Storage Cylinder Convert to Combi, Install New Combi£2000 – £25002 Days

Typically, system boilers work with an unvented hot water tank and provide hot water and heating. These are usually installed in larger properties having multiple bathrooms.

However, if you want to change a system boiler to a combi boiler, this will involve the removal of the DHW storage cylinder, conversion to a combi boiler and installing a new combi boiler, all of which will take around two days and cost between £2,000 to £2,450.

In conclusion, if you have a conventional boiler in your home, then it may be a wise decision to change to a combi boiler because of all the advantages it offers. They are space saving, energy efficient and can save on operation costs. So, in short, upgrading to a combi boiler is an investment worth making.

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Last Updated on November 6, 2021


Author: Indra Gupta

Indra is an in-house writer with a love of Newcastle United and all things sustainable.

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