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Over 200 years of experience
And trusted in millions of homes across the UK
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6,500 expert
engineersSo we’re always ready to install your new boiler
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Up to 3 years' interest-free credit
Spread the cost with £0 deposit and no hidden fees
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Up to 12 years' warranty
So if anything goes wrong. we’ll get it sorted
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.
Getting a combi boiler is easy
Just pick your preferred method and we'll be in touch.
Our most popular option
At home
This is a great choice if you'd like to talk to a combi boiler expert face-to-face or want to change your boiler type or location.
Online quote
If you plan on getting a new combi boiler installed in the same location, then you can quickly and easily get a quote online.
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
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Advantages |
Disadvantages |
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Space saving – no need for a separate water tank |
Pressure problems – functionality depends on mains |
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Neater looking – everything is hidden away in one unit |
Solo use – the flow rate drops if you want hot water in more |
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Easily serviced – they’re so popular, most engineers are |
Limited choice – power showers aren’t an option with a combi |
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Instant heating – you get hot water when you want it without |
Moving parts – because the boiler unit has moving parts, |
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Cheaper maintenance – generally the integral heating and |
Solar incompatibility – most, but not all, combi boilers aren’t |
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Energy efficient – new models boast over 90% efficiency |
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Money saving – energy efficiency also means lower bills |
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Easy installation – there’s just one unit to fit, and no extra |
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Safer water – you get water straight from the mains, so it’s |
Simple ways to pay for your new combi boiler
Monthly payments
Get up to 3 years' interest-free credit with £0 deposit (0% APR).
One single payment
Secure with a 10% deposit and pay the balance after your system boiler is installed.
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 |
10+ |
2-3 |
28-34kW |
4+ |
20+ |
3+ |
35-43kW |
Why 1000s choose British Gas to install their combi boilers
We're the UK's top boiler installer, fitting over 200,000 boilers every year. With British Gas, you're in safe hands.
We stock the best combi boiler brands
We’ve got a huge range of combi boilers from some of the top manufacturers, including Glow-worm and Ariston. And we’ll give you impartial advice to help you find the right combi boiler for your home.
What our customers think of us on 
The two engineers were absolutely fantastic - they explained what they were going to do and did exactly that, working all day! They filled me with so much confidence. And before leaving they explained again everything they'd done and left my home spotless.
The engineers came to remove the old boiler and fit the new one. The next day they did a Powerflush on the whole central heating system. After it was up and running, the old boiler and rubbish was removed and the engineer explained how to use Hive, set up the times for me and let me do it myself so I'd feel confident with it. Great service!
The Heating Adviser called me before they arrived. They had good customer skills and excellent knowldge of combi boilers. Her recommendation was emailed to me 3 hours after the visit - I was very grateful!
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.
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.