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Combi boilers heat water on demand and suit smaller homes. System and regular boilers use a hot water cylinder and suit larger homes with higher hot water demand.
✓ How each type works
✓ Which suits which home
✓ Thinking ahead to a heat pump
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Heats water on demand. No cylinder or tank needed. Best for smaller homes with one or two bathrooms.
Works with a hot water cylinder. Good for homes with more than one bathroom.
Uses a cylinder and a loft tank. Often found in older homes with existing systems.
A combination boiler, usually called a combi, heats your central heating and your hot water in one compact unit. When you open a hot tap, the boiler fires up and heats water straight from the mains, so there is no stored hot water to run out and no need for a cylinder or a cold water tank in the loft.
That makes a combi a space saver and often the simplest option for a flat or a smaller house. The trade-off is that it can only heat so much water at a time. If two showers run together, or a bath is filling while someone uses the kitchen tap, the flow at each outlet can drop.
A system boiler heats the radiators directly and sends hot water to a separate cylinder, where it is stored ready for use. Many of the main parts are built into the boiler, so there is no need for a feed and expansion tank in the loft.
Because hot water is stored, several taps and showers can run at once without the flow dropping, which suits a family home with more than one bathroom. The cylinder needs somewhere to live, usually an airing cupboard, and once it has been used it takes a little time to reheat.
A regular boiler, sometimes called a heat-only or conventional boiler, also works with a hot water cylinder, but it relies on tanks in the loft to feed and top up the system. It is common in older properties that were built or converted with a traditional setup.
Regular boilers cope well with a busy household and can be a sensible like-for-like replacement where the existing pipework is in good order. They need more space than a combi, and the loft tanks add to the installation.
The right choice depends on how many bathrooms you have, how many people use hot water at the same time, the space you have and the pressure of your mains water. A combi relies on good mains pressure, so it is worth checking this before you commit.
Think about how your household will change too. If you plan to add a bathroom or extend, a boiler with a cylinder may serve you better. If you are thinking about a heat pump in future, a system with a cylinder may make that transition easier, because a heat pump also needs a cylinder.
Changing type is often possible. Many people move from a regular boiler to a combi to free up the loft and airing cupboard, and some move the other way when a growing family needs more hot water. It depends on your water pressure, your hot water demand and the pipework you already have.
We assess all of this at a survey, so you know what is involved before you decide. Our guide to the cost of a new boiler explains what affects the price of a project, and our boiler installation page sets out how we work.
Can’t see your question? Send us an enquiry using the form at the top of the page and we will come back to you.
Often yes, but it depends on your water pressure and hot water demand. We check at the survey.
Efficiency depends on the boiler and how you use it more than the type. A correctly sized, well-controlled boiler matters most.
A system boiler with a cylinder usually copes better when several people use hot water at once.
Usually yes, so a system boiler with a cylinder can be a useful stepping stone.
Call 07549 400152 or send an enquiry online.
