Most of us use central heating daily without ever thinking about what’s actually happening behind the walls. This guide explains how does central heating work, covering the main components and how they work together to heat your home.
The Core Components of a Central Heating System
- Boiler – heats water, typically fuelled by gas, oil, or electricity
- Pump – circulates hot water around the system
- Radiators – release heat into each room
- Thermostat – controls when the system switches on and off based on temperature
- Programmer or timer – sets when heating runs throughout the day
How Water Moves Through the System
Water is heated in the boiler, then pumped through pipework to radiators around the home. As it passes through each radiator, it releases heat into the room before returning to the boiler to be reheated, in a continuous loop known as a wet central heating system.
Combi vs. System vs. Conventional Boilers
A combi boiler heats water on demand, without needing a separate cylinder, making it space-efficient for smaller homes. A system boiler uses a hot water cylinder but no separate cold water tank, while a conventional (regular) boiler uses both a cylinder and a loft-mounted tank, better suited to larger homes with higher hot water demand.
Fuel Types Behind the Boiler
Most UK homes use a gas boiler, installed and serviced by a Gas Safe registered engineer. Homes off the gas grid often use oil central heating instead, serviced by an OFTEC-registered engineer, while a growing number of homes are switching to electric heat pumps as a lower-carbon alternative.
The Role of the Thermostat and Controls
A thermostat measures room temperature and signals the boiler to switch on or off accordingly, preventing the system from running constantly. Smart thermostats and smart boiler controls add scheduling flexibility and remote control via an app, on top of this basic function.
Why Radiators Sometimes Need Bleeding
Air can become trapped in radiators over time, creating cold spots, usually near the top. Bleeding a radiator releases this trapped air, allowing hot water to fill the space fully and restoring even heat distribution.
Improving System Efficiency
A well-maintained, correctly balanced system heats a home more efficiently and cheaply than a neglected one. For practical ways to reduce your overall heating costs, see our guide to heating a house for cheap.
Frequently Asked Questions
Why is my radiator hot at the bottom but cold at the top?
This usually indicates trapped air, which can be released by bleeding the radiator with a radiator key.
What’s the difference between a combi and a system boiler?
A combi heats water on demand with no cylinder, while a system boiler uses a hot water cylinder but no loft tank, suiting different household sizes and hot water needs.
How long does central heating usually last?
A well-maintained boiler typically lasts 10-15 years, though this varies by model, usage, and how regularly it’s serviced.
