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Witten by Bernard Morgan (Engineer).
First Published: January 29, 2024. Updated: February 8, 2024

Types of Boiler – What do you have? Combi, System or Heat-only

There are three main types of boiler: combi, system and heat-only (also known as conventional or regular) boilers. Each has unique characteristics and serves slightly different needs.

When it comes to choosing the right boiler for your home, it is essential to ensure efficient heating and hot water.

Below is an overview of these boiler types, their workings, advantages, and disadvantages. We hope to help you decide whether to maintain your current system or opt for a new one.

Types of Boiler – Summary

Combi boilers offer space-saving benefits and instant hot water, making them ideal for smaller households.

Heat only boilers suit homes with traditional radiator systems, offering low replacement costs.

System boilers, with integrated components and unvented hot water cylinders, are best for properties with high hot water usage.

Understanding Boiler Types

Viessmann Vitodens 200-W - Types of boiler | BoilerhutWhat is a combi boiler?

Combi (combination) boilers integrate heating and hot water in one unit. They eliminate the need for hot water storage and provide hot water on demand.

This boiler type is ideal for homes with limited space. They offer efficiency and lower maintenance costs. However, combi boilers may not suit properties with low water pressure or high simultaneous hot water demands.

Learn more about combi boilers here >

What is a system boilers?

System boilers share similarities with regular boilers, such as working with hot water cylinders. They differ by having integral components like pumps and valves, making them a more modern solution.

These boilers suit homes with high hot water demand, providing good flow rates if mains pressure is adequate. However, they require more space than combi boilers and depend on strong mains pressure for optimal performance.

Learn more about system boilers here >

What is a heat only (conventional) boiler?

Heat only boilers, also known as regular or conventional boilers, require a separate hot water cylinder and cold water header tank. They are compatible with traditional open-vented heating systems but can also work on sealed systems.

These types of boilers are a cost-effective option for replacing existing systems. Especially if you don’t want significant changes. They work well with older radiator systems. However, their pressure isn’t as good as combi or system boilers.

Learn more about heat only boilers here >

Choosing the Right Boiler

Considerations for selecting a boiler type:

  • Properties with old radiators or specific installation constraints may benefit from sticking with a heat only boiler.
  • Homes with high simultaneous hot water use might consider a system boiler with an unvented cylinder, provided the mains water pressure is sufficient.
  • Budget constraints often dictate replacing the existing boiler with a similar type to minimise installation complexities and costs.
  • Those seeking low maintenance and operational costs should consider a combi boiler, especially if equipped with a long manufacturer warranty and if the home’s water pressure supports such a system.
  • Extensions or additional bathrooms could necessitate switching to a system boiler to meet increased hot water demands.
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Identifying Types of Boiler

Combi boiler - Types of boiler | Boilerhut

Combi Boiler

No hot water cylinder or cold water storage tank. Suitable for small to medium-sized properties with one or two bathrooms. Check for five copper pipes from the boiler.

They are gas, fresh cold water, hot water out, flow to the radiators, and return from radiators. Some combi boilers will have a sixth, thin copper pressure relief pipe that terminates outside.

A benefit of some boilers, including Viessmann Vitodens boilers is that the pressure relief pipe terminates into the condensate pipe reducing pipework.

System boiler - Types of boiler | BoilerhutSystem Boiler

Has a hot water cylinder but no cold water storage tank or external pump. Look for three copper pipes from the boiler. They are the gas, hot water out and return. Ideal for larger homes with two or more bathrooms.

The heating system is pressurised, so there will be a pressure gauge on the front of the boiler.

Regular Boiler

Heat only / Conventional boiler - Types of boiler | BoilerhutFeatures both a hot water cylinder and a cold water storage tank, along with an external pump. Two pipes from the top and one from the bottom of the boiler indicate a regular boiler, commonly found in older, larger homes.

Back Boiler (bonus boiler type)

Located behind the fireplace, these are now outdated and inefficient. Replacement with a system or combi boiler is recommended.

Type of fuels

The type of fuel you have doesn’t affect your type of boiler. Combi, system and regular boilers can use gas, LPG, oil or be powered by biomass. An air source heat pump isn’t powerful enough to power a combi boiler.

The exception to this rule is electric boilers. They won’t have a gas pipe feeding into them, so you can remove one pipe from each of the above examples if you think it might be electric.

Final Thoughts

Your choice of boiler will significantly impact your home’s comfort and energy efficiency.

It’s essential to assess your current and future needs, consider water demand, space availability, and budget.

Whether maintaining your existing setup or upgrading to a new boiler type, thorough research and professional advice can ensure you make an informed decision that meets your household’s heating and hot water requirements efficiently.

Still unsure?

If you are still unsure and you have the make and model of your current boiler to hand, a quick search online will tell you what type of boiler it is.

If this doesn’t help you, we can. Contact us or call us on 029 2009 9898 with the details of your boiler and we will identify what it is, and what we recommend to replace it.

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