Combi Boiler

A combination boiler that provides both central heating and instantaneous hot water without a separate cylinder, taking up minimal space.

A combi boiler heats both your radiators and your hot water on demand, with no separate hot water cylinder. Mains pressure water flows through a plate heat exchanger inside the boiler, heated as it passes through. Examples include Worcester Bosch Greenstar 4000, Vaillant ecoTEC plus and Viessmann Vitodens 100-W.

Pros: compact, no airing cupboard required, lower installation cost (£2,000-4,000 in Cornwall), and zero standing heat losses. Cons: limited simultaneous hot water (one shower at a time, typically 12-15 L/min for a 30kW combi), poor compatibility with low-pressure properties (under 1.5 bar mains), and you cannot easily integrate solar thermal or heat pump pre-heat.

For 2-3 bed Cornwall properties with a single bathroom and decent mains pressure, combi is usually the right choice. For larger families or properties with multiple bathrooms, a system boiler with cylinder is better. See our boiler installation page or call 01209 596 002.