Save on your energy bills with a new combination boiler

Buying a new combination boiler (combi boiler) could help improve your home's efficiency and cut your energy bills by up to 22%. And British Gas is here to help you find the right combi boiler for your home.

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What is a combi boiler and how does it work?

What is a combination boiler?

A combi (short for combination) boiler is the most compact option because it generates both your heating and hot water from a single unit, usually wall hung. With a combi boiler, there’s no need for a separate hot water tank.

How do combination boilers work?

Combi boilers are connected to the mains cold water supply and can heat water on demand. They burn fuel when you ask for hot water and have an integral heat exchanger that then gets hot enough to instantaneously heat the cold water from the mains supply as it flows over it.

Is a combination boiler right for my home?

Combi boilers can be cheaper to run compared to other boilers. But whether a combi boiler is right for your home all comes down to how much hot water you need and when. If you generally don’t need hot water in more than one place at once, then a combi boiler is great. But if you often need hot water to do the washing up while someone else is having a shower then a combi boiler wouldn’t be any cheaper than a regular boiler.

Is a combination boiler right for me?

A combi boiler is the right type of boiler for you if you have:

A small household
Only one bathroom
No loft to put a hot water tank in
10 radiators or fewer

Advantages	Disadvantages
Space saving – no need for a separate water tank	Pressure problems – functionality depends on mains pressure, so they won’t work as well if you have poor flow rates or incoming water pressure
Neater looking – everything is hidden away in one unit	Solo use – the flow rate drops if you want hot water in more than one place, so they’re not a great idea if you have more than one bathroom and people often shower at the same time
Easily serviced – they’re so popular, most engineers are trained to work on combi boilers so it’s easier to find someone to help if something goes wrong	Limited choice – power showers aren’t an option with a combi boiler because they rely on a hot and cold water feed from a gravity-fed system
Instant heating – you get hot water when you want it without waiting for a tank to heat up	Moving parts – because the boiler unit has moving parts, there is more potential for things to go wrong
Cheaper maintenance – generally the integral heating and hot water functions are covered by the manufacturer’s warranty	Solar incompatibility – most, but not all, combi boilers aren’t compatible with solar water heating systems
Energy efficient – new models boast over 90% efficiency
Money saving – energy efficiency also means lower bills
Easy installation – there’s just one unit to fit, and no extra water tanks to worry about
Safer water – you get water straight from the mains, so it’s safer and fresher than if it had been stored in a tank

Choose how you want to pay for your new boiler

A range of loan options²

Up to 3 years interest free (0% APR or up to 10 year 9.9% APR ³) all available at £0 deposit – subject to status.

Or pay in full

Pay just 10% today and the rest after installation.

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What size combi boiler should I have installed in my home?

The right combi boiler for you depends on a few factors including the type of property and the number of bedrooms and bathrooms it has.

Bedrooms	Bathrooms	Radiators	Recommended output
1-2	1	0-10	24-27kW
3-4	2-3	10+	28-34kW
4+	3+	20+	35-42kW

Why choose British Gas to install a new system boiler for your home

Our A-rated energy efficient boilers can save up to 22% on your gas bills ¹.

A range of loan options ² (up to 3 years interest free 0% APR or up to 10 year 9.9% APR ³) all available at £0 deposit – subject to status
5-year British Gas warranty - with all parts and labour included ⁴
Gas Safe certified installation by a Which? Trusted Trader
System water treatment and system cleanse included
Waste collection, recycle or disposal included
Carbon Monoxide Detector and Room Thermostat included

Find your new boiler

We stock the best new system boiler brands

At British Gas, we partner with top system boiler brands, including Vaillant, Worcester and many more. And we’ll give you impartial advice to help find the best system boiler for your home.

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Frequently Asked Questions

How do I bleed my radiators if I have a combi boiler?

When it comes to bleeding radiators, it’s no different if you’ve got a combi boiler or a conventional or system boiler. It’s important to do it every so often to keep them working efficiently, so you’re not wasting energy and money to heat them up. Here’s how to do it:

Turn off your heating and hot water and wait for the radiators to cool down
Use a radiator bleed key on the bleed point of a radiator and turn anti-clockwise
You’ll hear air escaping – this is normal
Let all the air out and once the hissing stops, close the valve

That’s how to bleed radiators for your combi boiler at a glance. For more information, take a look at our guide.

Learn more on how to bleed your radiator.

How do I turn down the combi boiler flow?

First, take a look at your combi boiler. There should be a heating knob at the front – if you’re not sure which one it is, you’ll find these details in the manual.

1. Keep turning the knob until it shows the maximum flow temperature

2. Next, start turning it down slowly. When the screen on your combi boiler shows 55 degrees, that’s when to stop. This is the best temperature as this is when your combi boiler is most efficient

You can control the temperature this way on your combi boiler. Turn it down if you just need to keep your home warm in the cold weather. Or up it by a few degrees to find the perfect flow temperature.

Can I leave a combi boiler on all the time?

You can leave your combi boiler on all day if you like, and it won’t cause any damage. As long as it’s plugged in and on standby mode, your combi boiler is raring to go but won’t actively be heating your home. If you keep your heating on all day, then this will impact your energy bill.

What's the optimum temperature to set a combi boiler?

For a combi boiler, you can set different temperatures for your hot water and your radiators. The optimum output temperature for radiators is 75°C. For the water it’s between 50 °C and 60 °C. The higher the temperature is set, the quicker your combi boiler will heat up.

How does a thermostat work with a combi boiler?

Thermostats and combi boilers work together to heat your home to the temperature you want. The thermostat has a sensor to detect your home’s temperature. It then ‘talks’ to the boiler – so if you set the thermostat to 19°C and your home’s temperature is 17°C, the thermostat tells your combi boiler to turn on and start heating up the radiators. Once the temperature reaches 19°C, it tells the boiler to turn off.

How can I adjust the water temperature on a combi boiler?

On a combi boiler, check the settings to find out how to change the water temperature. Combi boilers are split by tap and radiator temperature so you can change the temperature for each separately. Some combi boilers even have an image of each to make it crystal clear you know which one to adjust.

Is it safe to turn off a combi boiler?

Generally, it’s safe to turn off your combi boiler at the mains. However, depending on the age and type of your combi boiler. it could affect the heating when it’s turned on again if it’s left off for a long period of time.

Additional information

Savings based on an electricity price of 24.5 p/kWh and a gas price of 6.29 p/kWh, calculated from a weighted average of projected, current and recent energy price caps. The estimate applies to a semi-detached, gas-heated home upgrading from a D-rated boiler to a new A-rated boiler (with a programmer, room thermostat and thermostatic radiator controls (TRVs)). Actual savings will vary depending on the size and thermal performance of your home.
British Gas acts as a credit broker, not the lender and offers products from a panel of lenders. Payment options are subject to change without notice. British Gas is a trading name of British Gas New Heating Limited (No. 06723244), an appointed representative of British Gas Services Limited (No. 03141243) which is authorised and regulated by the Financial Conduct Authority (Financial Services Register No. 490568). Both companies registered in England and Wales. Registered office: Millstream, Maidenhead Road, Windsor, Berkshire SL4 5GD. Availability of credit depends on status and credit checks. Terms and Exclusions apply.
Representative example for 120 month order: Cash price: £2,503 | Deposit: £0 | Loan amount: £2,503 | Loan period: 10 years | Monthly repayment: £32.36 | Total amount payable: £3,883.20 | APR: 9.9%.
An annual boiler service is needed to keep your warranty valid. Boiler warranties range depending on the model.