Shop high-performance combi boilers from trusted brands at Toolstation, including Vokera, Ideal Boilers, Vaillant, Viessmann and Baxi. Whether you need a small combi boiler for your home or an industrial combi boiler for the workplace, we’ve got plenty of products available.

What is a Combi Boiler?

A combi (combination) boiler gives you heating and hot water straight from one compact unit. No tanks, no cylinders – it heats water as you need it. Perfect if you want to save space and keep the job simple.

What size combi boiler do I need?

It depends on the job:

Small homes or flats (up to 10 rads) – go for 24–27 kW
Medium homes (up to 15 rads) – 28–34 kW
Bigger jobs with more bathrooms – 35–42 kW

Get it right and you’ll have enough hot water and heat without overworking the boiler.

Are combi boilers energy‑efficient?

Yes. Most new combis are A‑rated and run at 90%+ efficiency. That means less fuel wasted and lower bills. Fit it right, set it up properly, and it’ll run efficiently.

Are combi boilers suitable for flats or small homes?

Yes. Combi boilers are built for places where space is tight. With no need for a hot water cylinder, you can fit one neatly in a cupboard or kitchen unit.

How long do combi boilers last?

On average, combi boilers 10–15 years with regular servicing. Look after it, flush the system when needed, and replace worn parts early to keep it running longer.

What Is the Best Combi Boiler?

If you’re wondering how to choose the right combi boiler, there are a few factors to consider. As a general rule, the more hot water you use, the higher the kilowatt rating you’ll need. For example, if you live in a flat or house with up to ten radiators and one bathroom, a 24-27kw combi boiler is the ideal choice. For homes with up to fifteen radiators and two bathrooms, a 28-34kw combi boiler is best. Large homes or businesses with up to twenty radiators and two or more bathrooms should opt for a 35-42kw boiler. Combi boilers are often the most energy-efficient choice in any central heating system, with options available to suit all budgets and home configurations. Check out our Boiler Buying Guide for more details on these and other boilers.

24KWW Combi Boilers

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