Guide to Household Boilers

Boilers and Heating

A Guide to Household Boilers

Your boiler is the heart of your home, supplying warmth through your central heating system and warm water through your taps. But finding the right one can be a challenge.

This guide to household boilers will help you find the right central heating system for you, your family and your home.

Jump to a topic using the links below:


The vast majority of household boilers run on mains gas. There are three types of gas boilers, they are:

  • Combi Boilers
  • Heat Only
  • System Boilers

A Gas Safe registered engineer will be able to tell you the most appropriate system for your home. Your engineer will consider your heating needs, such as your mains water supply and the age of your existing heating system.

Baxi Combi Boiler

Combination Boilers (Combi Boilers)

The most popular type of domestic boiler is a combi (combination boiler). Combi’s require little space and remove the need for large water tanks. Additionally, combi’s are economical because they rely on mains water pressure to supply hot water and heating on demand.

How Combination Boilers Work

Let’s say you set the thermostat to 21c; when the temperature falls below 21c, a signal is sent to the boiler. The signal tells the boiler to fire up and pump heat into the central heating system.

Once the heating climbs back to 21c, the boiler will regulate the heat to keep the room at the correct temperature.

The boiler diverts heat into the hot water supply when a hot water tap is turned on. The valve returns to the central heating when the tap is turned off.

Combi boilers can only direct heat to the central heating system or the hot water taps. It cannot do both at the same time.


Pros of combi’s

  • Energy efficient as they don’t need to constantly heat a hot water cylinder.
  • On-demand hot water, so you don’t need to wait for a hot water cylinder to refill.
  • Compact size – ideal for small homes
  • They don’t require a cold water tank
  • Combi boilers allow you to expand your heating system easily, so adding additional heating zones or hot water outlets is simpler.

Con’s of combi’s

  • Water flow will lose pressure if used at multiple points simultaneously. As a result, combi’s are less effective in larger homes.
  • Reliant on good water pressure from the mains.
valiant heat only boiler

Heat only (Regular Boilers)

Heat-only boilers are also known as conventional, regular and open-vent boilers. Heat-only boilers are popular in large properties as they can simultaneously produce hot water across multiple outlets.

It does not produce hot water for showers or baths.

How heat-only boilers work

Heat-only boilers work by heating water that is stored in a tank, which is typically located in a separate utility room or basement. The water is then circulated through a network of pipes to radiators throughout the home. As the water passes through the radiators, it releases heat, which warms the room.

Heat-only boilers use natural gas, oil, or electricity as fuel sources. When the thermostat signals that the temperature in the home has dropped below the set point, the boiler will turn on and begin heating the water. The heated water is circulated through the radiators until the desired temperature is reached. The boiler will continue to operate until the thermostat signals that the set point has been reached, at which point it will turn off until the temperature drops again.

Heat-only boilers are typically less efficient than other types of boilers, such as combi boilers, because they do not produce hot water on demand. Instead, they heat and store a large volume of water, which can result in higher energy costs.


Pros of heat only

  • A good solution for older heating systems that require moderate pressure.
  • Heat-only boilers are relatively simple in their design and operation. As a result, maintenance and repair are often easier than other boilers.
  • They are ideal for larger properties as they provide greater water flow to multiple outlets.
  • It can be used with an immersion heater to provide a backup hot water supply.
  • Compatible with various heating systems such as radiators, underfloor heating and solar.

Con’s of heat only

  • It may lack compatibility with more modern heating systems
  • Requires a large amount of space to store a hot water cylinder.
  • Heat-only systems are more complex and expensive to install.
  • Limited control over the hot water temperature.
  • Typically less energy efficient than other types of boilers.
System Boiler

System Boilers

System boilers are typically found in larger homes with more significant heating and hot water demands than smaller dwellings. A system boiler uses a cylinder to store hot water. As a result, there is a constant supply of hot water ready to be distributed throughout a property.

How system boilers work

System boilers operate using either natural gas, oil, or electricity as a fuel source. When the thermostat signals that the temperature in the home has dropped below the set point, the boiler will turn on and begin heating the water.

The heated water is then circulated through the radiators until the desired temperature is reached. The boiler will continue to operate until the thermostat signals that the set point has been reached, at which point it will turn off until the temperature drops again.


Pro’s of a System Boiler

  • They work with a large hot water cylinder that stores hot water until you need it.
  • System boilers work with solar thermal systems
  • You can run multiple taps at the same time whilst maintaining pressure.
  • Faster hot water recovery time means they can produce hot water quickly.
  • System boilers heat radiators quickly and efficiently.
  • System boilers typically run quieter than other types of boilers as they don’t have a large pump or expansion vessel.


Con’s of a System Boiler

  • System Boilers use more space than combi boilers, using more of your living space.
  • If the boiler has been off for a while, it can take a long time to heat the hot water tank. Furthermore, the hot water can run out.

Boiler Brands

Choosing a boiler brand can be a daunting task for homeowners. Your household boiler is a significant investment, and you are correct to research the market before buying.

Choosing a reputable manufacturer is one of the safest ways to ensure your investment is good. Therefore, we will introduce you to some of the best-known boiler brands in the UK.


Worcester bosch logo

Worcester Bosch

Worcester Bosch is the market leader and continues to be the most installed boiler manufacturer in the UK. Worcester Bosch is rated “excellent” by Trustpilot with 4.6 stars out of 5 and over 33,000 reviews.

The company supplies combi, system boilers and regular boilers and is based here in the UK. Furthermore, Worcester received a Royal Warrant for providing boilers to the late Queen’s Sandringham estate. 

Vaillant logo


Vaillant is an international company that supplies boilers to more than 20 countries worldwide. The company develops and manufactures its boilers in the UK and across Europe and China and was incorporated in 1874.

Vaillant is rated 4.6 stars on Trustpilot and boasts 17.780 reviews. In addition, Vaillant specialises in gas boilers in the form of combi’s, system boilers and regular boilers.

Ideal Boilers Logo


Ideal was founded in 1906 and has over 100 years of providing boilers across the UK. Ideal boilers come highly recommended by third parties such as Which? and Good Housekeeping. 

Ideal Heating has the highest Trustpilot rating of manufacturers in this list, with 4.8 out of 5 and 24,000 reviews. They also provide a complete range of boilers suited to households and warranty options of up to 12 years!

Baxi logo


Baxi has been operating for over 150 years in the UK and Ireland. The company is known as an affordable boiler brand that provides good quality. In addition, Baxi has a Trustpilot rating of 4.5 from more than 46,000 reviewers.

Baxi Website

Viessmann logo


The Viessman Group is an international boiler manufacturer. The company is a family-run business and has been for four generations. Viessman has the smallest number of reviews, at just 3,775. However, they have accrued a rating of 4.3 out of 5 and are the leading manufacturer worldwide.

Viessmann website


How do I choose the right boiler for my home?

Choosing the correct boiler will ensure a warm home and a constant hot water supply. Conversely, a poor choice of boiler can lead to higher energy bills and a lack of hot water and heating.

We’ve listed our top 6 considerations when buying a new boiler.

  1. Size: Choosing an appropriately sized boiler for your home is essential. A boiler that is too small may not be able to meet your heating and hot water needs, while a boiler that is too large may be inefficient and waste energy.
  2. Fuel type: Boilers are available in various fuel types, including gas, oil, and electricity. You should choose a fuel type that is readily available and cost-effective in your area.
  3. Hot water demand: Consider how much hot water your household uses on a daily basis. If you have a large home with high hot water usage, you may need a boiler with a higher output or a combi boiler that can provide hot water on demand.
  4. Space: Think about the area you have available for a boiler and any associated tanks or pipes. If you have limited space, consider a combi boiler, which does not require a separate hot water cylinder or cold water storage tank.
  5. Budget: Determine your budget for a new boiler and consider the upfront and long-term costs, including the purchase price, installation costs, and ongoing energy costs.
  6. Energy efficiency: Look for a boiler that is energy efficient to save on energy costs and reduce your carbon footprint.

As with any large purchase, it’s a good idea to consult a qualified heating engineer or plumber who can assess your needs and recommend the best boiler for your home. They will be able to consider factors such as the size and age of your home, your hot water and heating requirements, and the fuel type available in your area.

Cost of installing a household boiler

The cost of buying and installing a new boiler can vary dramatically, ranging from £1500 to £4000. There are a number of factors that impact the price of a new boiler installation. They are as follows:

  • The type of boiler you choose – combi’s, regular and system boilers all require varying types of installation. As a result, costs are due to the installation’s complexity.
  • Boiler manufacturer and specification. Is it a like-for-like swap, or are you changing the boiler type?
  • If it is a brand new installation – for example, a boiler is installed in a different location than your existing boiler.

In addition, labour costs vary depending on the installer you use and the area you are based. For example, a boiler installation in London and Essex will vary from Manchester and Yorkshire.

Where to find a good boiler installer

Finding a reliable boiler engineer is essential to a high-quality boiler installation. Not only does a good installer provide a fast and efficient service, but they will also ensure your boiler is running at optimal performance. Performance is everything when it comes to boilers, and good efficiency saves money on energy bills while preventing the need for unnecessary repairs and servicing.

Frequently Asked Questions

We have been asked many questions about domestic boilers as a team of professional heating engineers. We have answered some of our most frequently asked questions below.

How long do boilers last?

A modern boiler that is well-maintained can last between 10 and 15 years. However, the lifespan of a domestic boiler can vary depending on several factors.

To ensure the longevity of your boiler, you should ensure your boiler is serviced annually to prevent unnecessary wear and potential breakdowns.

Poorly maintained boilers are susceptible to dirt build-up and corrosion, which can significantly decrease the lifespan of your boiler.

What is a condensing boiler?

Condensing boilers were designed to be an energy-efficient alternative to older boilers. Their efficiency comes from how the boiler captures and uses heat that would usually be lost through the flue, the pipe that carries harmful gases out of your home. Condensing boilers achieve this by using a special type of heat exchanger that removes as much heat as possible from the flue gases before releasing them into the atmosphere.

Does a new boiler need a gas safety certificate?

Yes, a new boiler typically needs a gas safety certificate before it can be used. A gas safety certificate, also known as a gas safety record or a Landlord Gas Safety Record, is a document that proves that a gas appliance, such as a boiler, has been checked by a qualified gas engineer and is safe to use.

The purpose of the certificate is to ensure that gas appliances are correctly installed and maintained and that they do not pose a risk of gas leaks or carbon monoxide poisoning.

In the UK, it is a legal requirement for landlords to have gas appliances, including boilers, inspected and tested by a qualified gas engineer at least once a year and to provide tenants with a copy of the gas safety certificate.

This applies to new boilers as well as older models. It is also a good idea for homeowners to have their boilers checked by a qualified gas engineer at least once a year to ensure that they operate safely and efficiently.

Can I have a boiler installed in my bedroom?

It is generally not recommended to install a boiler in a bedroom. Boilers produce heat, noise, and exhaust gases during operation, and it is generally more comfortable and safer to have them in a separate utility room or basement.

In addition, specific regulations may prohibit the installation of a boiler in a bedroom. For example, in the UK, the Gas Safety (Installation and Use) Regulations 1998 state that gas appliances, including boilers, must not be installed in a room used as a bedroom or a space where people usually sleep. This is because gas appliances can produce carbon monoxide, a toxic gas produced when fuels such as gas, oil, or wood are burned. Therefore, if a boiler is installed in a bedroom, there is a risk that carbon monoxide could accumulate in the room and pose a risk to the occupants.

If you are considering installing a boiler in your home, it is essential to consult with a qualified heating engineer to determine the best location for the appliance and to ensure that it is installed in compliance with regulations.

Is a System Boiler cheaper than a Combi?

The cost of a system boiler and a combi boiler can vary depending on a number of factors, including the size of the boiler, the brand, and the specific features and technology it includes. Combi boilers are typically more expensive than system boilers because they are more efficient and provide hot water on demand.

However, it is important to note that the initial cost of a boiler is only one part of the overall cost of operating a heating system. The efficiency of the boiler, as well as the cost of fuel, will also affect the overall cost of running the system.

Combi boilers are generally more efficient than system boilers because they do not require a separate hot water storage tank, which means they can save energy and reduce fuel costs. On the other hand, system boilers may be a more economical choice for larger homes or homes with high hot water demand, as they can produce hot water more quickly than combi boilers.

It is also essential to consider the installation and maintenance costs when comparing the cost of different boilers. A qualified heating engineer can help you choose the best boiler for your home and budget and can estimate the installation and maintenance costs.

About the author

Trades Team are experts in Heating, Plumbing and Gas Services. We have 15 years of experience providing expert Boiler Repair and Boiler Servicing to homes and businesses across the Southeast. Learn more about Trades Team.

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