Which type of boiler is right for my home?

If your boiler is due for replacement, the first decision is which type to fit: a combi, a system boiler or a regular boiler. The short answer is that it depends on how many bathrooms you have, how much hot water your household uses at once, how strong your mains water supply is, and what system you have now. A combi suits most smaller homes, while busier homes with more than one bathroom often do better with a boiler that stores hot water in a cylinder.

This post explains how each type works, the homes each one suits, what changes if you switch from one to another, and why the hard water in our part of Cambridgeshire is worth thinking about too. Choosing and fitting a gas boiler is a job for a Gas Safe registered engineer, but knowing the options helps you ask the right questions.

The three types of boiler in plain words

• Combi boiler: heats water straight from the mains as you turn on a tap, and heats your radiators too. There's no hot water cylinder and no tanks in the loft.

• System boiler: heats your radiators and a hot water cylinder, usually in the airing cupboard. Most modern cylinders are "unvented", which means they run at mains pressure and don't need a cold water tank in the loft.

• Regular boiler (also called a conventional or heat-only boiler): works with a hot water cylinder and one or two tanks in the loft that feed the system. It's common in older homes.

When a combi boiler makes sense

A combi is often the best fit for flats and homes with one bathroom. Because it heats water on demand, you never run out of hot water, and you free up the airing cupboard and the loft.

The limit is how much hot water it can make at once. A combi works well when one shower or tap is running, but if two people shower at the same time, both will notice the flow drop. It also depends on your mains water: if the pressure or flow coming into the house is low, a combi can only deliver what the mains supplies. An engineer can measure this at a survey.

When a system boiler is the better choice

A system boiler suits homes with two or more bathrooms, or households where several taps and showers often run at once. The cylinder holds a store of hot water, so a shower upstairs isn't affected when someone runs a bath.

The trade-offs are space for the cylinder and the time it takes to reheat. If the store runs out, you'll wait a while for it to heat up again. An unvented cylinder also needs fitting and servicing by an engineer with a G3 qualification, the qualification for working on unvented hot water systems, and a yearly check of its safety valves. Our post on unvented cylinder servicing explains what that involves.

When to keep a regular boiler

If your home already has a regular boiler with tanks in the loft, and the system works well, replacing it like for like is often the simplest and least disruptive choice. It can also suit older homes with older pipework, which may not cope well with the higher pressure of a combi or unvented system.

Regular systems are less common in new installs, because the loft tanks take up space and the hot water pressure is usually lower, especially on upper floors.

What changes if you switch type

Swapping a regular boiler for a combi is a popular upgrade, but it's a bigger job than a like-for-like replacement. The loft tanks and the cylinder come out, pipework is altered, and older radiators and joints that were happy at low pressure may need checking. Going the other way, from a combi to a system boiler, means finding room for a cylinder and running new pipework to it.

Either change takes longer than a straight swap and costs more, so it's worth weighing what you'll gain against the disruption.

Why hard water matters when you choose

The water around Ely and Littleport is hard, which means it carries a lot of dissolved minerals. When hard water is heated, those minerals form limescale. In a combi, the small plate heat exchanger that heats your tap water can scale up over time, leading to hot water that runs lukewarm or changes temperature. Cylinders and immersion heaters scale up too.

Whichever boiler you choose, it's worth protecting it. A scale reducer on the water supply to the boiler, or a water softener for the whole house, cuts the build-up. Our water treatment page explains the options.

What about homes off the gas grid?

Some homes out in the Fen villages aren't on mains gas. Oil boilers come in the same three types, and the same questions about bathrooms and hot water apply. Oil boilers need an OFTEC registered engineer rather than a Gas Safe one.

How we help you choose

At Beach Plumbing & Heating, we start with a survey. We look at the size of your home, your radiators, how much hot water you use and the strength of your mains supply, then recommend the type and size of boiler that suits. We're Gas Safe registered, G3 qualified for unvented cylinders, OFTEC registered and Worcester accredited, so we can fit any of the three types and, on eligible Worcester models, register an extended guarantee.

If you're thinking about replacing your boiler, arrange a survey with Beach Plumbing & Heating and we'll talk you through which type makes sense for your home. Our boiler installation page explains how we size, fit and commission a new boiler.