System vs Combi Boiler: What’s the Difference?

When it comes to choosing a boiler for your home, two of the most common types are system boilers and combi (combination) boilers. While both serve the same basic function — heating your home and providing hot water — they do so in different ways. Here's a quick guide to help you understand the key differences.

Combi Boilers: All-in-One Convenience

A combi boiler is a single, compact unit that heats water on demand. There’s no need for a separate hot water cylinder or cold water tank, making it ideal for smaller homes or properties with limited space.

Pros:

• Space-saving – No need for external tanks or cylinders.

• Hot water on demand – Heats water directly from the mains as you need it.

• Energy efficient – No energy wasted heating a tank of water.

Cons:

• Limited flow rate – May struggle if multiple hot water taps are used at once.

• Not ideal for large households – Best suited for homes with one bathroom.

System Boilers: Great for Bigger Homes

A system boiler works with a separate hot water cylinder to store hot water for use. Unlike combi boilers, it doesn’t require a cold water tank, as it takes water directly from the mains.

Pros:

• Better for high demand – Can supply hot water to multiple taps at once.

• Consistent pressure – Mains-fed system offers steady water pressure.

• Ideal for larger households – Good option if you have multiple bathrooms.

Cons:

• Takes up more space – Requires a hot water cylinder.

• Hot water isn't instant – Once the stored water runs out, you’ll need to wait for it to reheat.

Which One is Right for You?

• Small homes or flats with one bathroom? A combi boiler is likely the best fit.

• Larger homes with multiple bathrooms? A system boiler might be the better choice.

Ultimately, the right boiler depends on your household's size, water usage, and space availability. Consulting a heating engineer can help you decide based on your specific needs.