All You Need to Know About Gas Boilers & Central Heating

What is a Gas Boiler?

Essentially, a boiler is like a big furnace or fire that’s controlled by your thermostat. The main function of a gas boiler is to act as a heater and provide buildings with the hot water they need, which is important for two very big reasons.

Firstly, the hot water produced by your boiler is pumped through your radiators when you turn on your central heating, providing them with a reliable source of heat. This keeps you warm and comfortable in the colder months of autumn and winter — and sometimes during spring and summer as well.

The second main function is providing a steady supply of hot water for your sinks, baths and showers. They do this by heating up a tank or container of water and keeping it at a consistent temperature, which means you can rely on the hot water you need to keep yourself (and your belongings) sparkling clean.

How Does a Gas Boiler Work?

While there are a variety of gas boilers on the market, they all work in much the same way — by heating gas to warm your home. This gas can enter the boiler via two different methods: by being connected to a main or through an LPG bottle.

The hot water produced by your gas boiler is then pumped through your central heating system, travelling via pipes into your radiators to heat your home. Depending on the type of boiler you own, this will either flow directly through taps and showers (combi), or will be transferred and stored in a separate water tank or cylinder (system and heat only).

What Does a Gas Boiler Do? Central Heating

Central heating works like a circuit – hot water is pumped from the boiler into each radiator in turn, and is in constant, or near-constant, circulation when the heating is switched on. Although you might need to top up the pressure in your radiators from time to time, the same water is used over and over again. 

By the time the water has passed through all the radiators, it will have lost some of its heat, but that is restored in the boiler and it is sent around again.

Whether or not central heating is “on” is determined by the thermostat, which helps the temperature of a home stay more or less constant, to within a few degrees either side of your chosen temperature.

What Does a Gas Boiler Do? Hot Water

The second job of the gas boiler is to heat water. It performs this task in the same way as it does for central heating, that is, through pumping circulated water over the flame so it heats up.

There are two ways it does this:

1. Instant hot water as in the case of the combi boiler

2. Heating water in a tank, like the system boiler or the heat only boiler

In both cases, however, the water that is heated over the flame is not the water that comes out of the tap – it is simply used as a medium for heating the water you use.

What’s Inside a Gas Boiler and How Does it Heat Water?

There are numerous components housed inside a gas boiler, including a gas burner, heat exchanger and a flue. Each element serves a specific purpose, working together to keep your home warm and provide you with a continuous, reliable supply of hot water.

Below are the main individual components, along with the functions they fulfill:

• A valve allows gas to enter the combustion chamber
• The gas burner works exactly how it sounds, by burning gas to produce the heat that’s required for your home and hot water
• The heat exchanger safely transfers heat to the water by passing it through a pipe within the heated gas chamber
• A pump or fan pushes this water out of the boiler and either into the system or a separate cylinder or storage tank
• A flue or waste pipe connects your boiler to an external part of your property. It is responsible for safely releasing the by-products produced by your boiler, including water vapour and carbon monoxide.

A central control board allows you to control your boiler

Do Gas Boilers Need Electricity?

Although it’s gas that heats the water in our boilers and keeps our homes warm, gas boilers actually do need a small amount of electricity to work too. That may sound strange, but electricity is simply used to help specific parts and mechanisms of our central heating systems function.

Electricity is used to power everything from the valve that opens to let gas flow into the combustion chamber, all the way to digital displays and smart thermostats like Ideal’s app-controlled Halo system.

How Do Combi Boilers Work?

Combi boilers are suitable for most small and average-sized households. They work by circulating hot water around the central heating system, and also heat up incoming mains water incredibly quickly when a hot tap is turned on. That means instant hot water, 24/7. They don't require storage tanks either, which means they take up hardly any space. 

A potential drawback is that if several people turn on different hot taps or showers at the same time, pressure and temperature of the water will drop as the heating capacity is exceeded. Also, since they rely on water mains pressure, they are unsuitable for areas of low pressure.

How Do Heat Only Boilers Work?

Also known as conventional, regular, open vent or traditional boilers, these systems heat water that circulates around the central heating system; a separate circuit heats up a hot water tank, warming up the water in the tank. The tank is fed by a cold water tank, usually in the loft, which is fed by mains water. This is the traditional type of boiler used in all homes before the 1970s.

Heat only boilers are useful for larger households, because once the tank is full of hot water, multiple taps can be run from them at the same time. The hot water tank can have electric elements installed to heat the water overnight when electricity is cheaper, or to act as a backup should the boiler break down. The main drawback is that once the hot water is used up (i.e. if someone has a deep bath), everyone has to wait for the water to re-heat again. They can also heat more water than is required, which is inefficient. 

How Do System Boilers Work?

System boilers are similar to heat only boilers; the main difference is that the hot water tank is fed by mains water, not water from a cold tank. They therefore use up less space, but have the same advantages and drawbacks as heat only systems.

How Long do Gas Boilers Last?

How long a gas boiler lasts depends on how well it’s cared for, but it’s generally best to replace it every 15 years. It’s not that they’ll suddenly stop working at this age, but this is the point where it becomes more cost effective to invest in a new model.

Gas boilers are complicated appliances that work around the clock to make sure we have hot water and heating, whenever we may need them. They work so hard to keep us comfortable that even the most reliable boiler parts will eventually fail.

Here at Ideal, our gas boilers come with warranties of up to 12 years. Simply register your warranty within 30 days — your installer may do this for you — to enjoy continual support and peace of mind.

Signs You May Need a New Gas Boiler

There are several signs to be aware of that may signal your trusty gas boiler is reaching the end of the road. It may be regularly breaking down or losing pressure, or you may notice unusual loud bangs coming from your central heating.

If your gas bills start to creep up unexpectedly, that’s another sign that your boiler is not operating efficiently. In all of these cases, we’d recommend calling out a Gas Safe engineer to cast an expert eye over it. It could be that there’s a simple solution, or they may advise you it’s time to invest in a new model.

For more information, visit our blog post on replacing an old boiler.