Different Types of Boilers are Explained: Combi, System, Heat Only

Are you looking for the perfect boiler for heating and hot water? To do that, knowing the types of boilers available on the market is essential for making the right choice for your home. If you don’t buy the correct type of boiler for your needs, you will be unsatisfied with it for the next 10–15 years.

The three most popular types of boilers used by homeowners in the UK are regular boilers (also known as heat only boilers), system boilers, and combi boilers. Each type of boiler is suitable for different types of properties with varying sizes and consumption patterns. It would help if you also chose the fuel type between an oil and gas boiler and an electric and gas boiler.

Knowing how each boiler works is important to keep getting hot water and heat without interruption and save money on your energy bills.

In this helpful guide, we’ll take you through the different types of gas boiler systems, explaining how they work and highlighting their main advantages and disadvantages. This way, you can decide on your new gas boiler installation or replacement.

The Different Types of Boilers Explained

Combi boilers, heat only boilers, and system boilers are all great ways to heat a home and ensure it has enough hot water. However, each boiler type does this differently and with different components.

All the different types of gas central heating boilers available on the market condense. Condensing boilers recover latent heat from flue gases, reducing energy waste while increasing energy efficiency. According to UK Government Regulations in 2005, which have set standards of performance of all boilers summarises that all new boilers installed after the 1st of April 2005 should be condensing.

Below, we are mentioning the different types of boilers and their functions. After reading about the types of boilers, you can identify which one you need the most.

Combi Boilers

What Is a Combi Boiler?

Combi boilers (or combination boilers) are the most popular heating system in the UK. Compact and highly efficient, these boilers are designed to provide instantaneous hot water and effective heating.

Unlike other gas boiler systems, combi boilers do not require additional storage tanks or cylinders. Their water is sourced directly from the mains, allowing them to provide hot water faster.

Related: All About Combi Boilers: How They Work, Types, Advantages & More

How do combi boilers work?

Combi boilers heat water directly from the mains using an integral heat exchanger. This heated water is then sent to your taps and radiators to provide heating and hot water on demand via the diverter valve.

Pros and Cons of Combi Boilers

Here are the main pros and cons of combi boilers:

Pros

• On-demand hot water: As combi boilers heat water directly from the mains, they can deliver hot water instantly.

• Compact: Most combi boiler systems are compact and typically small enough to fit into a standard kitchen cupboard. You also don’t need to worry about fitting any tanks or cylinders into your home with combi systems. This makes them an excellent choice for smaller homes where space is limited.

• Energy efficiency: combi boilers’ condensing technology helps reduce energy waste and the impact of heating on the environment.

• Savings: When using energy efficiently, installing a combi boiler can save up to 35% on energy bills.

• Long-lasting: When maintained effectively and regularly serviced, a combi boiler can provide you with quality heating and hot water for up to 15 years.

• The diverse range of options available Due to their popularity, many types of combination boilers is available for you to choose from. Many brands manufacture this type of boiler, with numerous capacities and models available.

Cons

• Not suitable for some homes – Combi boilers cannot deliver hot water and heating simultaneously, so you temporarily won’t be able to access your heating while running a shower or bath. This makes them a potentially unsuitable choice for larger homes with higher heating and hot water demands.

• Reliance on mains pressure: Combi systems source their water directly from your mains supply, and you’ll need to ensure that you have a decent quality of water pressure in your area. If the water pressure in your area is low, this can impede the performance of the combi boiler.

• It cannot be used with a power shower because it requires a water cylinder, which combi boilers lack. Also, the pump needed for power showers is incompatible with combi boilers.

The Verdict: Is a combi boiler the right choice?

The combi boiler is the right choice if you have a relatively smaller household with 1-2 bathrooms and 2-3 people requiring instantaneous hot water simultaneously. Its space-saving design makes more room in your home, and its efficiency saves you a lot of money on your energy bills.

Heat Only Boilers

What is a Heat Only Boiler?

Heat only boilers, known as regular or conventional boilers, are the traditional form of heating in the UK. This type of boiler provides hot water and central heating through an additional cold water tank and hot water cylinder for storage. Heat only boilers are particularly suitable for large homes as the stored water can be supplied to multiple taps simultaneously.

Related: What Are Heat Only Boilers? A Complete Guide

How Do Heat Only Boilers Work?

Water is fed into the cold water tank from the mains and then into the system’s hot water cylinder. The cold-water tank is usually stored in your loft.

The heat only boiler will heat the hot water cylinder in your airing cupboard to heat the water. This water is then supplied to your taps and radiators as needed.

Heat only boiler systems also feature a feed and expansion tank to help maintain the system’s water levels. This extra component is required as water is often lost from the system due to leaks or evaporation. The feed and expansion tank will replace the lost water to help ensure that the water pressure remains constant.

Pros and Cons of Heat Only Boilers

Here’s a breakdown of the main pros and cons of heat-only boilers:

Pros

• Can provide hot water to multiple taps simultaneously. As hot water is stored in a cylinder, heat only boilers can distribute hot water to more than one tap simultaneously, so you can run a tap while someone else takes a shower. This makes them ideal for large properties with high hot water demands.

• Quick and easy to install: If your property already has a traditional heating system installed, fitting a new heat only boiler should be short and straightforward.

• Compatible with immersion heaters: A backup immersion heater could be installed with your hot water cylinder to help ensure access to hot water even if your boiler system faces a breakdown.

• Not reliant on mains pressure Unlike combi boilers, heat only systems are not dependent upon the water pressure supplied by your mains. This means you can receive great-quality hot water regardless of the water pressure in your local area.

Cons

• No space-saving option: heat only boilers can be unsuitable for smaller homes due to their additional cold-water tank and hot water cylinder. You must ensure you have the space in your loft for these different components.

• Hot water is not delivered on demand. Unlike combi boiler systems, the hot water produced by heat only boilers is not instantaneous. Once the hot water from the system’s cylinder has been used, you’ll need to wait for it to heat up again.

• Heat can be lost; heat only boilers are generally less efficient than combi boilers. The stored hot water can lose heat over time, and energy has to be used to heat the water back up. To help improve efficiency, you can insulate your hot water cylinder with an insulating jacket.

The Verdict: Is a heat only boiler the right choice?

If your home’s water supply is low-pressure, heating only with a boiler may be the ideal choice. But remember that you must make ample space in your home for the storage tanks.

If your home requires more hot water at multiple taps, then it is more space-efficient and energy-efficient to buy a system boiler instead of a heat only boiler.

System Boilers

What is a System Boiler?

A system boiler is a gas boiler that provides heating and hot water using an additional hot water cylinder. Unlike heat only boilers, system boilers do not require a cold-water tank, as most of their heating components are already built into the system. They are excellent for homes with high heating and hot water demands.

Related: What Is A System Boiler? Everything You Need To Know

How do system boilers work?

Within a system boiler unit, water is heated via the heat exchanger in an enclosed hot water system. Hot water is then distributed directly to your radiators to provide your property with heating. Hot water is also sent to the cylinder for storage and to your taps when required.

Pros and Cons of System Boilers

Below, we outline system boilers’ main pros and cons to help you choose the right type of boiler for your home.

Pros

• Can provide hot water to multiple taps simultaneously. System boilers are recognised for meeting high hot water demands. They store hot water in a cylinder and distribute their supply to multiple taps simultaneously.

• They occupy less space than a heat only boiler. As this type of boiler does not require a cold-water tank, it is more space-saving than heat only boilers.

• It can be fitted with a backup immersion heater. Like regular systems, system boilers can have a backup immersion heater fitted to their hot water cylinder in case of a boiler breakdown.

• Compatible with renewable energy sources: system boilers’ storage cylinders can be heated using solar panels. This can help to improve your heating system’s energy efficiency.

Cons

• Less space-saving than combi boilers: As combi boilers do not require additional tanks or cylinders, they can help save more space than system boilers, which require a hot water storage cylinder.

• Hot water is not instant—unlike combi boilers, system boilers do not source their water directly from the mains. This slightly slows down the hot water delivery process, and you may have to wait for the water to heat up.

The Verdict: Is a system boiler the right choice?

Suppose you have a bigger home with 3–4 bathrooms and 5–6 people requiring hot water and heating simultaneously. In that case, a system boiler is the ideal choice compared to heat only boilers, as they are more space- and energy-efficient.

But if we talk about system vs combi boilers, combi are more energy efficient and space-saving, and not to forget, they are suitable for smaller homes.

Conclusion:

We hope this article has made you knowledgeable about which type to choose. Still, if you are confused about which boiler to choose or whether to buy a new boiler or replace an old one, contact us at 0345 3192 247. Our team of professionals at customer support will answer all your queries and help you get the ideal boiler that best suits your needs.

FAQs

What type of boiler do I have?

The best way to determine the type of boiler you have installed is to examine the system closely. For example, if you have a combi boiler installed, you will see no extra tanks or cylinders, plus you’ll notice five copper pipes coming from the bottom of the system.

If you have a heat only boiler, you will notice an additional tank and cylinder connected to your system. Plus, there will be two copper pipes that come from the top of the boiler system and one coming from the bottom of the system.

Finally, if you have a system boiler installed, you should be able to identify a hot water cylinder but no cold-water tank. Additionally, you should see three copper pipes coming from the bottom of the system boiler unit.

What is the best type of boiler to buy?

The best type of boiler for your property will depend on the size of the home and the scale of your heating and hot water needs. Combi boilers are the most popular type of boiler available in the UK. Combi boilers are regarded by many as the best type of boiler to buy due to their compact dimensions, energy efficiency, and high quality of heating and hot water.

What type of heating is a combi boiler?

A combi boiler is a gas boiler with energy-efficient condensing technology. This system burns fuel to provide heating. However, it recovers latent heat from flue gases to improve efficiency.