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System Boiler Vs Combi Boiler

System Boiler vs Combi Boiler – Which Is Best?

Buying a new boiler can be exciting, frightening or even just a frustrating process. Before you can decide on the perfect boiler model for your home, you must first decide on the type. Perhaps you have narrowed your selection down to a system or combi boiler. This guide will run you through the differences between these two types of boilers, while also analysing their pros and cons.

What is the difference between a system and combi boilers?

A system boiler receives cold water directly from the mains supply, which is then heated by a heat exchanger. Next, the water travels to the hot water cylinder, where it will be stored until it is required.

Although a system boiler works with a hot water cylinder, it does not need the additional space for a cold water tank, as regular boilers do. A combi boiler has no need for either, as these efficient boilers take water from the mains and heat it, providing instantaneous hot water and heating from a singular unit.

System Boilers Pros

System boilers can supply a higher water demand than combi boilers, as water can be stored in reserve, within the hot water cylinder. As these boilers do not work alongside a cold water tank, it is not essential to own a property with a loft. System boilers have a built-in pump which means they can respond to water demands quickly, resulting in the fast track delivery of pre-heated water. These boilers are also compatible with solar panels, enabling them to generate power to heat the water in the hot water cylinder.

System Boiler Cons

Even though system boilers do not need a cold water tank, their requirement for a hot water cylinder, means they take up more space than combi boilers. The amount of hot water you can use depends on the quantity of water readily available in the hot water cylinder. Once this water runs out, you will then have to wait for the cylinder to heat back up. If the hot water cylinder is not insulated properly then the water will lose heat, damaging the boiler’s efficiency.

Combi Boiler Pros

If you are replacing an old boiler, then you will be pleased to know that combi boilers have far better energy efficiency ratings than older boiler models. Their unrivalled efficiency allows you to reduce your energy usage and save money on your energy bills. As combi boilers provide heating and hot water from a single unit, they take up less space and are easier to install than other types of boilers. Combi boilers can also produce hot water extremely quickly, as there is no need for a separate water tank.

Combi Boiler Cons

Combi boilers can only supply a relatively low water demand; therefore, they are generally only suited to homes with one bathroom. To get the best out of this boiler, you need good mains pressure, otherwise, the taps will produce a poor water flow. As there are no additional water tanks with a combi boiler, if the unit breaks down then you will be stuck without hot water and central heating.

Which one is best?

Unfortunately, there is not an outright favourite between system and combi boilers, with both types having their own pros and cons. The efficiency of combi boilers generally makes them cheaper to run, however, they struggle to supply high water demands. Therefore, to ensure you make the right choice, you should align your property size with each boiler’s traits. For example, a couple living in a flat with one bathroom will have the level of water demand that perfectly suits a combi boiler. Whereas a house with more than three bedrooms and multiple bathrooms will make the system boiler a better option, as they will need the pre-heated supply to cope with the demand for hot water.

Worcester Bosch Boiler

Homeowners are still able to get a FREE boiler grant or insulation grant via the ECO scheme, which is still available to households that qualify. Warma UK are currently working throughout the UK helping privately owned and rented homes to improve home energy efficiency and save money on rising energy bills.

For more information email –

Or call 03304600065

Apply For Your Government Backed Heating Grant

Following your successful application, we will arrange a free, no obligation survey to ensure the maximum grant is obtained and advise you on the best products to reduce your homes energy usage.

Michael Cornish