Boilers & heating

IN THIS GUIDE

Combi vs system vs heat-only

Combi boilers heat water on demand with no tank — ideal for smaller homes and flats. System boilers use a hot-water cylinder — better for larger homes and multiple bathrooms. Heat-only (regular) boilers suit older homes with existing tanks. Match the type to your hot-water demand.

What a new boiler costs

A new gas boiler is typically £2,000–£4,000 installed, depending on brand, type and whether it is a straight swap or a system change. A like-for-like combi swap sits at the lower end; moving position or changing type costs more.

What size (kW)

Combi boilers are sized by hot-water demand: roughly 24–27 kW for a small home or one bathroom, 28–34 kW for a typical family home, and 35–42 kW for larger homes with two or more bathrooms. Oversizing a combi wastes money; too small and showers run cold when a tap is on.

Brands & warranties

Worcester Bosch, Vaillant, Viessmann and Ideal are the mainstream reliable choices; premium models come with longer warranties (up to 10–12 years) if fitted by an accredited installer and serviced annually. A longer warranty is usually worth paying a little more for.

Boiler or heat pump?

Before replacing a boiler like-for-like, weigh a heat pump: with the £7,500 grant the upfront gap narrows, and running costs can be lower on the right tariff. If your boiler has died and you are not ready, a new boiler buys time — but insulate now so a heat pump is easy later. See the heat pump guide.

Running costs & controls

Whatever you fit, good controls cut bills: a smart thermostat, weather compensation, and turning the boiler’s flow temperature down (to about 60°C for a combi) all improve efficiency. Annual servicing keeps it safe and on-warranty.