Which type of boiler is right for my home?

If you're replacing an old boiler, the first question is usually which type to choose: a combi, a system boiler or a regular boiler. The short answer is that it depends on how many bathrooms you have, how many people need hot water at the same time, and what's already in your airing cupboard and loft. A combi suits most smaller homes with one bathroom, while busier homes with two or more bathrooms often do better with a system or regular boiler and a hot water cylinder.

This post explains how each type works, which homes each one suits, and what a heating engineer looks at before recommending one. Choosing the type is your decision, but fitting a boiler is always a job for a Gas Safe registered engineer, so use this as a guide to the questions to ask rather than a plan for the work.

How a combi boiler works

A combination boiler, or combi, heats your radiators and your hot water from one compact unit. It has no hot water tank. When you turn on a hot tap, it heats mains water instantly as it passes through.

That makes it a good fit where space is tight, with no cylinder in the airing cupboard and no tanks in the loft. You also never run out of hot water, because nothing is stored.

The trade-off is flow. A combi can only heat so much water at once, so if someone runs the shower while someone else fills a bath, both will notice. How well a combi copes depends on its output and on the pressure and flow of the mains water coming into your home, which is why an engineer should check the incoming supply before recommending one.

How a system boiler works

A system boiler heats your radiators directly and heats your hot water through a separate cylinder, a large insulated tank usually kept in an airing cupboard. Most of the working parts, such as the pump, are built into the boiler, and there are no tanks in the loft.

Because hot water is stored, several taps and showers can run at once at good pressure, especially with an unvented cylinder, which is fed straight from the mains rather than from a tank in the loft. The catch is that once the stored hot water is used up, the cylinder needs time to heat up again.

A system boiler suits homes with two or more bathrooms, and households where several people shower at the same time each morning.

How a regular boiler works

A regular boiler, also called a conventional or heat-only boiler, works with a hot water cylinder and two tanks in the loft: a cold water storage tank that feeds the cylinder, and a smaller feed and expansion tank that keeps the heating topped up.

Many older homes were built with this setup. Because the water is fed by gravity from the loft, pressure at the taps can be lower, especially upstairs, unless a pump is added.

A regular boiler is often the sensible choice where the existing pipework was designed for it, or where older radiators and pipes might not cope with the higher pressure of a sealed system.

Which type suits which home

As a rough guide:

• One bathroom, one to three people, short on space: a combi is usually the simplest choice.

• Two or more bathrooms, or several people needing hot water at once: a system boiler with a cylinder usually copes better.

• An older home with tanks in the loft and original pipework: a regular boiler may be the least disruptive, though changing to a system boiler is often possible.

• Weak water pressure or flow from the mains: a combi may struggle, so stored hot water is often the better option.

Think about the next ten years too. A new bathroom, a growing family or a loft conversion can change the answer.

Should you keep the type you have now?

Not always. Swapping like for like is usually quickest and causes the least disruption, but it isn't automatically right. Changing from a regular boiler to a combi frees up the airing cupboard and the loft, but means new pipework and won't suit a home with two busy bathrooms. Going the other way means finding room for a cylinder.

If you might want a heat pump one day, it's worth knowing that heat pumps work with a hot water cylinder. Keeping your cylinder space, rather than removing it for a combi, can make that change easier later.

Rules a new gas boiler has to meet

In England, every new gas boiler must reach at least 92% efficiency under rules known as Boiler Plus, and must be fitted with time and temperature controls, such as a programmer and a room thermostat. A new combi must also come with at least one extra energy-saving measure, such as a smart thermostat that learns how your home heats up, or weather compensation, which adjusts the boiler's output to the temperature outside. Our guide to the benefits of smart heating controls explains how these work.

An unvented cylinder must be fitted by someone qualified to install unvented systems, because it stores hot water under pressure and relies on safety valves that have to be set up correctly. All gas work, including fitting the boiler itself, must be done by a Gas Safe registered engineer.

What we check before recommending a boiler

At 7 Day Plumbing Services, a boiler installation starts with a survey of your home. We look at the size of the property and how much heat it loses, the existing pipework and cylinder, where the flue can go, and how much water your mains supply delivers. We also ask how your household uses hot water. You then get a written proposal setting out the boiler type and size we recommend, the controls, the timescale and the paperwork you'll receive.

If your current boiler has stopped working this winter, a repair may keep you warm while you decide. Our boiler repair service can tell you whether it's worth fixing.

There's no single best type of boiler, only the one that fits your home and the way you use hot water. If you're weighing up a new boiler, 7 Day Plumbing Services can survey your home and recommend the right type and size. You can book a survey through our boiler installation service.