Boiler Replacement

Combi Boiler [Costs + 10x Benefits]

Are you looking for a compact boiler that heats your home and gives you warm tap water? Opt for a combi boiler.

In this article you will find comprehensive information about this versatile boiler.

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What is a combi boiler?

A combi boiler is a heating device that delivers warm water to the central heating as well as warm tap water. Because it combines two functions in one unit it is called a combination unit.

Combi boilers eliminate the need for a separate hot water cylinder.

Different fuels

There are different fuels to heat your home with. These are:

  • Gas
  • LPG
  • Oil
  • Electric

Gas combi boiler

Gas is the most popular fuel for boilers these days. But to run your boiler on gas, you need to be connected to the National Gas Grid. Because gas combi boilers are the most popular choice, there is a wide range to choose from.

Almost all of the boiler brands produce gas powered combi boilers.

They are also on average cheaper than LPG and oil boilers, as you can see under the heading ‘What is the average price of a combi boiler?’.

LPG combi boilers

LPG is a kind of gas that is used to run boilers in homes that are not connected to the National Gas Grid. A supplier delivers the LPG on a regular basis to an on-site tank.

An LPG tank needs continued filling and maintenance which makes it more time-consuming and expensive than a gas combi boiler. More about the costs under the heading: ‘What is the average price of a combi boiler?’.

But in places that have no connection, it is a good alternative to gas.

Oil combi boilers

Oil is a popular fuel for boilers. This is because combi boilers that run on oil are more energy efficient and have emissions that meet UK regulations.

Oil fuel like LPG, needs to be supplied by a local oil supplier, which makes it more cumbersome than a gas boiler. But if your home isn’t or cannot be connected to the National Gas Grid, oil is a good alternative.

Oil combi boilers are a bit more expensive than gas and LPG boilers. For more information about the costs, go to the heading ‘What is the average price of a combi boiler?’.

Electric combi boilers

Electric combination boilers are a relatively new type of boiler. If your home is not connected to the National Gas Grid, an electric combi boiler can be a good alternative. It can also be a good alternative to LPG and oil, because an electric combination boiler is tankless.

Electric combi boilers are also quieter in operation than the other boilers.

But there is also a drawback… Electricity is more expensive than the other fuels, so the electric boilers can be more expensive to run.

Are you looking for the right kind of combi boiler for your home? Ask boiler installers for advice and get free boiler quotes.

How does a combi boiler actually work?

A combi boiler consists of different parts that work together to heat your home (central heating) and tap water. Combi boilers can heat your radiators and water-based floor heating with a few adjustments.

The most important parts of a combi boiler are the heat exchangers. They are the heart of the operation.

A combi boiler consists of two heat exchangers:

  • Primary heat exchanger
  • Secondary heat exchanger

Roughly, a combi boiler works as follows:

  1. When you buy a new boiler, you buy a condensing one. These condensing boilers are more energy efficient than non-condensing. When the water is heated, it needs fuel. When non-condensing boilers produce heat, they also produce warm flue gases which are not used. With the new condensing combi boilers this wasted heat gets recycled, by the Flue Gas Heat Recovery System (FGHRS). This way the new combi boilers are more energy efficient. A non-condensing boiler has 60 to 70% energy efficiency. With a condensing boiler the energy efficiency is 90 to 100%.
  2. The primary heat exchanger delivers hot water to the central heating system (in most instances, the radiators). The water gets recycled and streams back to the boiler. The water gets reheated and goes back into the central heating system. The primary heat exchanger works in tandem with a thermostat.The water inside the central heating gets dirty over time, so the central heating water is not used as tap water.
  3. The secondary heat exchanger is used to deliver on-demand tap water. A combi boiler doesn’t deliver water from a tank, but it draws it directly from the main. The secondary heat exchanger heats the water and delivers it when there is a demand.

Pressure expansion vessel

A combi boiler is a sealed vent system. This means the system is closed. When the central heating water is heated, it expands. Because the sealed vent system can take a certain amount of pressure, it needs an expansion vessel.

This vessel regulates the excessive pressure, so the central heating system will not be damaged.

When the water cools down, the excessive water from within the expansion tank will flow back into the central heating system.

Do you want to save space, energy and installation costs? Ask a boiler installer to install an energy efficient combi boiler. Request free boiler quotes now.

What are the benefits of a combi boiler?

There are a lot of benefits to having a combi boiler. You will find a comprehensive list below.

1. More energy efficient

All the new combination boilers are condensing boilers. This means that the heated flue gas that is wasted in a non-condensing boiler is used by a condensing combi boiler to pre-heat the cold water entering the boiler.

2. Instant access in smaller properties

A combi boiler delivers almost instant warm tap water. You don’t have to wait for the tank to refill.

3. Costs less to install than other boilers

The installation costs of a combi boiler are considerably lower than a regular boiler with its extra pipework and cylinder.

4. Selling point

When you sell your home, a combi boiler can be a selling point. The new owner will have less maintenance costs and does not have to remove an old boiler.

5. Compact

A combi boiler is a compact piece of apparatus. It combines two units into one, which makes a combi boiler suitable for smaller homes and spaces.

6. Less pipework

A combi boiler central heating system needs less pipes than a regular boiler. Which makes the system easier to maintain. This makes this type of central heating less prone to problems.

7. Lower maintenance costs

Because a normal combi boiler system has no external tank, it takes less time to maintain. So the maintenance costs are also less than a regular boiler.

8. New builds

A combi boiler is the perfect solution for smaller and mid-sized new builds. And when your new build is sufficiently insulated, you can have a combi boiler with a lower kW. Which saves you money on energy.

9. Different fuel types

There are combi boilers available that can run on gas, oil, LPG gas or electricity. Even if you are not connected to the National Gas Grid, you can opt for an oil, electric or LPG combi boiler.

10. Cleaner system

Because there is no storage tank and there is less pipework, central heating systems with a combi boiler tend to be cleaner.

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What are the cons of combi boilers?

Unfortunately, there are also disadvantages to a combi boiler.

Not suitable for larger homes

A combi boiler is less suitable for larger homes with two or more bathrooms. There are combi boilers with higher flow rates, but in most instances a system boiler is the best option.

Long pipework

In some properties, when the boiler is a longer pipe’s length away, you have to wait a moment for hot tap water.

Water pressure

The mains water pressure in your home needs to be sufficient to run a combi boiler.

No immersion heater

A combi boiler doesn’t have an immersion heater. If the combination breaks down there is no immersion heater as a backup.

What is the price of a combi boiler?

A combi boiler is a relatively cheap boiler. The average price of a combi boiler is around £1000, excluding installation costs. For the information about the installation and total costs of a combi boiler, go to ‘What are the installation costs of a combi boiler?’.

Below you find the average prices (inc VAT) for the different combi boiler sizes (without the installation costs).

Gas combi boiler prices

Gas Avg. price
24kW £700
30kW £900
35kW £1,050
40kW £1,200

Oil combi boilers prices

Oil Avg. price
24kW £2,000
30kW £2,300
35kW £2,800

LPG combi boilers

Gas Avg. price
24kW £950
30kW £1,075
35kW £1,200
40kW £1,450

Electric combi boilers

Electric Avg. price
7 kW £900
11 kW £1,050
18 kW £1,150
24 kW £1,275

What is the average lifespan of a combi boiler?

A combi boiler lasts around 16 to 18 years. This is the economic lifespan. What does this mean?

After 15 years the combi boiler will run less efficiently, so the running costs will be higher. After the average lifespan, it is recommended to buy a new (combi) boiler.

The technical lifespan of a combi boiler can be longer, sometimes up to 25 years, but after the 15 years, the combination boiler will run less efficiently and the maintenance costs will be higher.

Is the hot water from a combi-boiler drinkable?

Yes, when the water comes directly from the mains it is drinkable, unless the central heating is made of copper pipes. In this case it is better not to drink the water directly from the tap.

Another exception is if the combi boiler uses a storage tank. Then it is not recommended to drink the water, even if the tank is cleaned on a regular basis.

Information about the installation of combination boilers

Do you want to know more about the installation of a combi boiler? Read on.

What are the installation costs of a combi boiler?

In the overview below you find the average installation costs. These are the prices without the boiler.

Combi type Avg. installation costs
Gas £400
LPG £400
Oil £1,000
Electric £1,100
Moving to
different space

Installation costs for combi boilers

Can a combi boiler be fitted in a bathroom?

It is possible to install a combination boiler in your bathroom. But there are a few precautions to consider:

Around wet areas: The boiler cannot be (re)located in close proximity to the bath / shower or the sink. This spot is called ‘zone zero’. The combi boiler can only be installed at a minimum of 2.25 meters above the zero zones and not within 0.6 meters on either side.

Electricity: The main electrical spur needs to be located outside of the bathroom.

Cupboard: It is strongly recommended or required to place the combi boiler in a cupboard, that is situated as far away as possible from the ‘zero zones’.

Ask boiler installers for advice about where to place your combi boiler. Get quotes from local boiler installers.

Can a combi boiler cope with two showers (running simultaneously)?

It is technically possible to run two showers with a combi boiler. But the water flow rate can be poor if you run the two showers simultaneously. In order to tackle this problem, you have to opt for a combi boiler with a storage tank.

When there is a demand, the tank can deliver warm water instantaneously.

Ask boiler installers which type of combi boiler is best suited to your needs and home.

Does the combi boiler have to be on an outside wall?

A combi boiler needs to be as close to an outer wall as possible. Preferably against the inside of an outer wall.

All new combination boilers are condensing boilers. Only in certain properties where a sealed vent system is not possible, an open vented is permitted. Open vented system are mostly situated in the heart of your home. But the seal vented systems are installed on the outside wall.

Regulations stipulate that the flue of sealed systems needs to be situated as far as possible from doors and windows

Ask a boiler installer where a combi boiler can be installed safely in your home. Get your boiler installer quotes today