Combi, system, or regular: which boiler suits the house

Most of the calls we take in Bradford are about a combi. It is the boiler people can see on the kitchen wall, and it is the one a lot of terraces were converted to. It is not the right boiler for every house. The choice is between a combi, a system boiler, and a regular boiler, and it follows the hot water, the space, and the mains, not the badge on the front.

A combi heats water as you use it

A combination boiler takes cold water from the mains and heats it when a tap or the heating asks for it. There is no hot-water cylinder and, on a straight combi, no tank in the loft. That is why it fits a smaller house, and why the installation is often simpler than a system that still needs a cylinder.

Hot water comes out at mains pressure. One shower, or a kitchen tap on its own, is usually fine. Two outlets at once are where a combi shows its limit. A shower and a bath running together, or two showers in a larger house, can leave both of them thin. Poor mains flow into the house does the same thing. If the cold tap in the kitchen is already weak, a combi will not invent pressure that the street main does not have.

A system boiler keeps a store of hot water

A system boiler heats a cylinder. You can draw hot water to more than one bathroom at the same time, because the water is already hot in the store, not being made one litre at a time as it passes through the boiler. That suits a family house where mornings overlap.

The trade-off is space, and a cylinder that loses some heat while it sits there. You need a cupboard for the cylinder. You do not need the old loft tanks that a regular boiler uses, unless the cylinder itself is an open-vented one. If the house already has a decent cylinder and more than one bathroom, ripping it out for a combi is often the wrong saving.

A regular boiler still uses the loft

A regular, or conventional, boiler is the older arrangement: a cold-water tank in the loft feeds a hot-water cylinder, and a separate feed serves the radiators. Plenty of older houses in Bradford, Leeds, and the rest of West Yorkshire still have that layout. It works. It also means tanks, pipework, and a cylinder to look after, and it is the layout people usually leave behind when the loft is being boarded or the tanks have failed.

Changing a regular boiler for a combi is a real installation, not a like-for-like swap. The tanks can come out, the flue may need a new route, and the hot water then depends on the mains. Say so on the phone if that is what you want. We will say if the house is better left on a system boiler with the cylinder kept.

What to tell us

• How many bathrooms are used at the same time
• Whether there is a cylinder, and whether there are tanks in the loft
• Whether the cold tap in the kitchen already runs slowly
• The make on the boiler, if one is already fitted

We fit combi, system, and regular boilers, including Baxi, Ideal, Main, Worcester Bosch, Vaillant, Glow-worm, Vokèra, and Potterton. The type is agreed before the day, along with removal of the old boiler, the flue, and the controls.