Heat Only (Regular) Boiler Explained: 24-40kw Guide

2 October 2026 · 4 min read

A heat only boiler, also called a regular or conventional boiler, heats water for your radiators and a hot water cylinder. It usually works with a cold water tank in the loft and a feed and expansion tank.

How it differs from a combi

A combi heats water on demand and needs no tanks or cylinder. A heat only boiler stores hot water in a cylinder, so several taps can run at once.

How it differs from a system boiler

A system boiler also uses a cylinder, but the pump and expansion vessel are built in and there is no loft tank.

Who should choose a heat only boiler

Larger homes with two or more bathrooms, older properties with gravity-fed systems, and homes where low mains water pressure makes a combi a poor fit.

Replacing like for like

If you already have a heat only boiler, replacing it with another is usually the simplest and lowest-cost option. We can also advise if converting to a system or combi makes sense.