How Much To Change From Water Tank To Combi Boiler

Last updated: November 15, 2023

Are you considering changing from a boiler with a tank, or maybe a system, immersion heater or conventional boiler? Is it possible and what are the costs involved?

In this guide we answer the most common questions regarding changing your current heating system to a combi boiler, as well as potential limitations.

Why change to a combi boiler?

First things first, why change to a combi boiler?

Typically, people change from a traditional heating system and/or type of boiler due to three main factors:

  • Modern combi boilers are extremely efficient (A-rated models can exceed 92% efficiency).
  • Combi boilers help conserve space as they don’t require separate tanks (including a cold or hot water storage cylinders).
  • They are typically much easier and cheaper to repair and maintain.

A combi (short for combination) boiler is a boiler designed to provide both hot water and central heating from a single unit.

It is able to provide hot water on demand, meaning that if you use your tap or heating, the hot water will be provided almost instantly.

This is a unique feature not found in boilers that utilise a hot water tank, in which case you would have to wait for the water to heat up before you can use it.

combi boiler works without a tank, instead it takes cold water directly from the mains water supply and heats it as and when needed.

As you turn your tap on, cold water will be drawn into the boiler where it’s heated up via the heat exchanger, which transfers the heat from the burning gas to the cold water.

In comparison to conventional boilers, the installation options for combi boilers are more flexible, since you do not have to install close by to a larger storage tank.

For this reason, they are preferred by those who have limited living space.

Average Costs to Change/Convert to a Combi Boiler

As with most things, the exact costs of converting from a conventional or system boiler depends on a variety of factors (detailed below).

However, on average changing from a conventional boiler (with a tank) to a combi boiler will cost somewhere in the region of £2,000 to £4,000 depending on the complexity of the installation.

Remember, it’s always advised that you get a variety of boiler quotes before making a final decision.

See also  WarmZilla Review - Boiler Buying Guide 2024

As mentioned the final costs can be impacted by a variety of factors, which include the following:

  • The type of boiler e.g. combi boiler, system or heat only.
  • The brand of the boiler.
  • The warranty length that comes with the boiler.
  • If you want the boiler moving to a new location in your property.
  • The location of the boiler e.g. in some cases scaffolding may be required, which can increase the price.
  • Any extras e.g. radiator’s, pipework, a power flush or thermostats.
  • Whether it’s an emergency call-out or not.

Benefits of Changing to a Combi Boiler

A combi boiler is suitable for most household properties in the UK, hence why they are the most popular type of domestic boilers used.

However, the reality is that they aren’t always suitable, here are the main things to bear in mind when considering your options:

A combi boiler is a suitable choice unless you have a high demand for hot water and heating where several hot showers are running at once or dozens of radiators. Here’s why:

Combi Boiler Efficiency

Modern combi boilers are extremely energy efficient, as we explain in our boiler ERP efficiency guide. In fact modern combi boilers are A rated, meaning that they are around 90% efficient.

In financial terms that means for every £1 you spend, only 10 pence is lost, that is extremely good compared to boilers just 10 years ago that were only 70% efficient.

This efficiency difference doesn’t just mean combi boilers are better for the environment as they release less carbon dioxide, but it also means they use and waste less fuel, meaning you will also save money when your energy bills are concerned.

Wondering which boiler manufacturers performed best? Check out our best boiler brands guide for the full rundown and if you are trying to determine who the best boiler installation company is, check out our Warmzilla and Boxt reviews.

Combi Boilers Save Space

If you have a property with limited space, a combi boiler is one of the most compact types of boilers, so it’s ideal for you.

See also  Best Boiler Brands/Manufacturers UK

In fact, some newer combi boilers are marketed as being “cupboard size”.

Conventional boilers are much larger on average and require a hot water storage tank since they do not provide hot water on demand, which itself takes up a considerable amount of space.

Additionally, combination boilers require less pipework than conventional boilers and are ideal for smaller and medium sized properties.

Lastly, they are typically much easier to service, install and repair, which also impacts installation and other associated costs.

What size boiler is right for your home? If you are thinking about a combi boiler, it is largely determined by the number of radiators in your home.

Check out our complete guide to new boiler installation here if you are wondering about the best type of boiler for your home. 

How much may a new boiler cost? Are you considering converting from a conventional to a combi boiler? Use our boiler installation cost calculator to get an estimation.

Less Risks of Repairs & Breakdowns?

Many people argue that since combi boilers don’t have as many moving components that have longer lifespans, and that they are easier to maintain and service.

Learn all about the different types of boilers, including condensing boilers, LPG boilers, oil boilers, Opentherm boilers and calculating boiler size in our guide.

Who isn’t a Combi Boiler Suitable for?

Combi boilers are the most common type of domestic boiler in the UK, so therefore, are suitable for most properties.

However, most homes are small to medium sized and in the case of larger homes with multiple bathrooms, a standard combi boiler is unlikely to be suitable.

Why are combi boilers not suitable for some homes?

Combi boilers heat cold water on-demand, directly from the mains water supply. They do not store any hot water via a hot water tank and so the flow of water can weaken if there is a high demand for hot water. 

This means that if you have multiple bathrooms in your home that are likely to be used simultaneously, a combi boiler may not be able to maintain a strong and consistent supply of hot water to both outlets.

See also  Guide To Replacing A Boiler With A Heat Pump

Additionally, some properties may be very old or have weak pressure coming from the mains, in which cases a combi boiler may not be advised.

The table below shows an indication of the type of boiler likely to be based on your property type (please bear in mind that this a crude estimation):

Property TypeIdeal Boiler 
Small Home
1 Bathroom
Combi Boiler
Small Home
2 Bathrooms
Combi Boiler
Average Size Home
1 Bathroom
Combi Boiler
Average Size Home
2 Bathroom
Combi Boiler
Average Size Home
3+ Bathroom
Regular/System Boiler
Large Home
1 Bathroom
Combi Boiler
Large Home
2 Bathrooms
Regular/System Boiler
Large Home
3+ Bathrooms
Regular/System Boiler

Wondering how much a new boiler costs? Check out our guide on options available if you need a new boiler but can’t afford it, as well as boilers on finance and government boiler grants here.

What Is Involved In Changing To A Combi Boiler?

As well as being more complicated than a normal combi boiler replacement, a conversion i.e. changing from an old system to a combi boiler installation requires more time, materials and labour and as a result, these factors can influence the final cost.

Remember not only is this job incredibly difficult for the newbie, it is not legal to carry out any type of work with a gas appliance unless qualified and registered to do so.

Therefore, getting your boiler installed by a registered gas safe engineer is crucial.

Things a Gas safe engineer does during a swap from the old type of boiler/system to combi include the following:

  • Cleaning the current central heating system.
  • Removing the current conventional boiler and storage tank.
  • Removing associated controls.
  • Inspect the existing pipework to determine if any faults can compromise the combi boiler.
  • Installation of the new combi boiler and any required pipework.
  • Powerflush on the entire boiler system and installation of magnetic filters or limescale filters for hard-water areas.
  • Installation of new smart thermostats that can help prevent energy waste.
  • Testing of the new combi boiler system to ensure it’s running correctly. The gas engineer will also provide tips on best usage and maintaining your combi boiler.

Did you know the efficiency of your boiler can impact the amount of energy it uses and ultimately impact your heating bill costs? Check out our guide to the best condensing boilers if you are interested to find out more.