Many homes and businesses are connected to the natural gas grid, and use this gas to heat their homes, produce hot water for taps, showers, and baths, and sometimes to cook with.

Worcester Gas Boiler on a wall
A Worcester gas boiler installed on a wall

Other types of heating and hot water systems exist; some more rural areas might use oil boilers or LPG. More modern homes, and those who want to reduce their carbon footprint, have moved away from fossil fuels, using ground or air heat pumps or biomass boilers to power their systems.

Gas boilers might not be the best choice environmentally, but the chances are you will have a gas central heating system in your home, so it is a good idea to understand as much as you can about it – from the names of the components to how it works. According to the ONS, 74% of homes in the UK use natural gas to heat their homes.

In this article we will take you through the basics of the system that you have in your home or business, name some of the components, and discuss how this connects to your radiators and is controlled by your thermostats.

Components of a Gas Boiler

Let’s start by defining some of the components that are in your gas boiler.

  • Burner: Where the mixture of gas and air ignites to produce a flame
  • Pilot Light: Small flame that remains alight constantly and is used to ignite the main burner.
  • Heat Exchanger: Transfers heat from the flame into the water.
  • Pressure Gauge: Shows that the pressure of the system is in safe working parameters.
  • Flame Supervision Device: Monitors gas supply; cuts gas supply if flame goes out to prevent gas leaks.
  • Gas Valve: Controls the flow of gas into the burner.
  • Thermostat: Signals the boiler to turn on and off as needed based on temperature in room.

Common Gas Boiler Types

There are three different types of gas boiler, and it should be reasonably simple to work out which one you have in your home or business.

  1. Regular/Standard Boiler

This is one of the older systems and consists of a heating and hot water system connected to a hot water cylinder. A regular gas boiler also needs a cold-water tank attached to maintain water levels and pressure.

  • System Boiler

In this system, you will have a gas boiler containing all the components and a separate hot water cylinder. These systems are designed to allow multiple taps to be in use at once without losing water pressure.

  • Combi Boiler

Potentially the most modern version of fossil fuel-based boilers, the combi boiler provides hot water on demand with no need for cold water storage tank or a hot water cylinder. It is also considered to be highly efficient.

Boiler Opened Showing controls
A boiler door opened to show the control panel

The Heating Journey

The heating system in your house probably has not changed much from the very earliest central heating systems – radiators and the boiler are connected on a closed loop, and the heating is provided using water. How that happens might seem like a bit of a mystery, but it is relatively simple.

Your boiler is designed to heat water steadily, which is then pumped around your home through each radiator.

To start with, the gas valve allows a certain amount of gas to travel into the burner from the mains supply. This then combusts with air thanks to the pilot light and creates a flame. In more modern boilers, combustion is achieved using an electric ignition switch.

The heat produced by the flame in the burner is then transferred to water using a heat exchanger. The water reaches a temperature of around 60°.

This heated water is then pumped through the system following a continuous circuit of pipe that joins every radiator in the system. Each radiator panel has part of this loop going back and forth (or up and down) through the radiator, which exposes the metal surface to more heat, making it easier to radiate heat into the room. The copper pipes behind the panel are bent at right angles, which produces the maximum area of heating surface.

After passing through all the radiators, the water returns to the boiler. At this point, it will have cooled down significantly so will need to be reheated to be sent onward again.

Controlling Your Heating

Obviously, you don’t want to have your heating on all the time – your house would soon be unbearably hot, even in the winter, and that is not even considering the sky-high energy bills that this would create.

Controlling heating is therefore very important, and there are a few ways you can do this.


Thermostats are usually found on the wall of one of the rooms in your home. These can be used in one of three ways:

  • Manual on/off: Turn the heating off and on as you need it.
  • Temperature Based: The thermostat monitors the temperature of the room and turns the boiler on and off depending on what the sensors are saying.
  • Time Control: Thermometers with this feature will automatically turn the heating on or off, depending what times you have set on the system.

Smart Thermostats

As with other home appliances and systems, there are an increasing number of smart thermostat systems being created. With these, users can control their heating using an app or even through their mobile phone.

Thermostatic Radio Valves

Thermostatic Radio Valves (TRVs) are a great way to ensure that the temperature of each of the rooms in the house is correct. You can set a TRV to heat a radiator less in rooms that do not get much use, or to increase heat to radiators in rooms that need a boost.

Got a Gas Boiler Question?

Here at GMS, we have Gas Safe-registered engineers on hand who can help you arrange everything from annual services to emergency repairs. If you are looking to upgrade your central heating system, or you want to reduce the carbon footprint of your home, then you might want to speak to our Renewables team, who will be happy to discuss options for systems like Air Source Heat Pumps. You can contact us today via email or on the telephone.