How do boilers work?

How do gas boiler systems work?

Your boiler is the heart of your central heating system. It sends hot water through to your radiators and taps to provide you with heating and hot water.

Gas boilers can be connected to the gas mains and get a continuous supply of fuel or they can have Liquid Petroleum Gas (LPG) cylinders that need to be periodically refilled. During operation, a valve connected to your boiler opens and gas enters into a sealed combustion chamber, an electric ignition system or permanent pilot then ignites to burn this fuel.

Hot jets that are linked to a heat exchanger within the boiler transfer heat to the water that flows over the exchanger. An electric pump then pushes the hot water through to your radiators and taps.

All new boilers are condensing. They are built with a heat exchanger arrangement that removes as much heat as possible from the flue gases. Condensing boilers recycle latent heat from the water vapour that is produced as a by-product of the heating process. This heat is then used to heat water that returns from your central heating system. These systems thus help to reduce energy wastage as less heat energy is required. By law, all modern boilers must be condensing.

How do the different boiler types work?

Although the basic process of burning fuel and sending water through to radiators and taps is the same with most boilers, each boiler type works differently.

Below we outline how each different boiler type works to provide heating and hot water:

Combi boilers

Combi boilers provide both heating and hot water to your home without any additional tanks or cylinders. They have two independent heat exchangers – one that connects to your radiators and one that links to your hot-water supply.

As no water tanks or cylinders are required, combi boilers are constantly on standby to provide hot water on demand. Once a request for hot-water or heating is made, these boilers will burn fuel which then causes the heat exchanger to heat water.

Combi boiler systems are built with control valves which operate in different directions depending on whether hot-water or heating is required – they therefore cannot provide both at the same time.

Heat-only/ conventional boilers

Heat-only boilers are the traditional form of home heating. They work with an additional cold-water tank and a hot-water cylinder for water storage.

These systems are also built with a feed and expansion tank, which brings in cold water to regulate the water levels. This tank helps deal with the expansion that occurs when the water is heated and also replaces any water that is lost because of evaporation or leaking.

The cold water tank is filled up with water from the mains supply. Once the boiler fires up, it will send hot water to either the hot-water cylinder or the radiators. As long as the cylinder has sufficient hot water within it, you should be able to access water from multiple taps at once.

These conventional boilers can also be fitted with a back-up immersion heater to provide you with access to hot water should you face a boiler breakdown.

System boilers

System boilers provide heating and hot-water using an additional hot-water cylinder. Most of their major heating components are already built in, so they do not require any storage tanks. They work in a similar manner as heat-only boilers, however they require less additional components.

System boilers are sealed pressurised systems. Cold water is sourced directly from the mains supply using a filling mechanism. This water is heated and sent to either the hot-water cylinder where it is stored, or to the radiators. When you need hot water, the system will send it to your taps.

Find the right boiler for your home and needs

We’re working together with BOXT, who can help you choose the best boiler for your home at the best price.

They install a range of combi, heat-only and system boilers from some of the industry’s leading brands. BOXT’s Gas Safe registered engineers could provide you with the help and advice you need to get quality heating and hot water in your home.

Get a new boiler