Components and Controls

Installing a Central heating system in your home is a big undertaking, but it is one that should be understood. Understanding the components of your central heating system and how it all works will help you seek help and advice when needed. Below is a list of the main components you will find to make up your central heating system:


The boiler is the main component of a central heating system. They come in many sizes and will deliver various amounts of heat energy, fuel types and energy ratings. The amount of heat energy (measured in kilowatts or kW) a boiler is required to deliver through the home is based on a series of calculations carried out by one of Central Heating’s technicians.


There are a wide range of boilers that burn a range of fuel types.

  • Natural Gas – Burns methane from the gas mains
  • LPG – Burns liquid petroleum gas, normally propane or butane
  • Biomass fuel – Burns wood logs, pellets or chippings
  • Electric – Works like a kitchen kettle but on a much bigger scale


  • Conventional boiler – This boiler is the most basic type. It burns fuel to make heat.
  • System boiler – This boiler provides central heating only or heating and a store of hot water in a hot water cylinder.
  • Condensing -This boiler uses the heat in the gases given off when the fuel is burnt.
  • Combination boiler – This boiler provides central heating and instant hot water.


There are many types of radiator. Most are made out of steel but there are copper and aluminium options available. A radiator works by transferring heat to the air in the room as it passes over the radiator panel. Warm air rises and pushes colder air back down and over the radiator surface again.


Underfloor heating is a set of plastic pipes that are often run under a solid concrete floor surface and use the floor itself to heat the room, by radiating heat upwards.


These work by using heated water passing through tubes that have a fan blowing air past them to heat the air up.


Pipes for central heating systems can be either copper or plastic, and come in many sizes from 8mm to 35mm in diameter.


This is used in a sealed central heating system to control expansion in the pipes and radiators. As the water is heated its volume increases by about 4%, the expansion vessel is designed stop parts of the system from bursting.


This valve is also part of the ‘sealed’ heating system. It is designed to operate if there is a problem with the expansion vessel or the system is over pressurised. This operates to remove pressure from the system.


A header tank is also known as a ‘feed and expansion’ tank. Its job is to top up your central heating system with water, and if your system overheats it provides somewhere for the hot water to go. It is part of an ‘open’ heating system.


The pump pushes the heated water around. It is usually located inside the boiler but can also be found in your airing cupboard.


This valve is responsible for choosing where the water from the boiler goes. The valves have a motor attached to the top so they are able to control the flow of heating water to either the central heating or hot water system.


Controls are the brains of the central heating system, with sensors and valves. The controls make the system work.


A boiler will usually have a dial on it, marked in numbers or from Min to Max. This sets the temperature of the water that will be pumped from the boiler through the radiators to heat your home.


The programmer/timer controls the flow of hot water to the radiators or hot water cylinder (if fitted), and it also decides to turn the system on or off depending on the temperature in the rooms and the time of day.


Individual room thermostats in your house measure the temperature of the air in the room, if it is cold it will tell the central heating to turn on, when it gets too warm it tells the central heating to turn off. Room thermostats need a free flow of air to sense the temperature, so they must not be blocked by curtains or furniture, or put near heat sources.


The TRV senses air temperature around them and turns the radiator on or off and regulates the flow of water through the radiator they are fitted to. They do not control the boiler directly.