A condensing combi boiler is one of the highest efficiency boiler you can buy in the UK at the moment.
This is the most complete guide on the internet when it comes to a condensing combi boiler.
If you’re still confused between the two, let us make it easier for you.
First things first:
All boilers manufactured in the last 10 years are condensing boilers.
So, whether you buy a boiler, or a boiler + installation from us or from any other manufacturer/heating company, you can be rest assured that you will be purchasing a condensing combi boiler.
To learn more, pick from any of the topics below:
- What is a Combi Boiler?
- How Does a Combi Boiler Work?
- How does Condensing Technology Work?
- When Should You switch to a Combi Boiler
- Which Boiler is Best for Your Property?
- What is a Storage Combi Boiler?
- Combi Boiler Efficiency
- Combi Boiler Reliability
- How much is a New Combi Boiler?
- New Combi Boiler Installation Cost
- Best Combi Boilers
- Most Energy Efficient Combi Boilers in the UK
- Buy a Combi Boiler Online
Condensing Combi Boiler Efficiency
55% of what you spend in a year on energy bills is spent on heating.
According to the Energy Saving Trust: “Heating accounts for about 55% of what you spend in a year on energy bills, so an efficient boiler makes a big difference.” The biggest reason for modern combi boiler efficiency in 2018 is down to condensing boiler technology.
How is Efficiency for a Condensing Combi Boiler Calculated?
“Seasonal Efficiency of Domestic Boilers in the UK” or SEDBUK is used to compare and classify boilers on energy efficiency. Combi boilers are measured on how good they are at converting fuel to heat.
There are two different types of SEDBUK ratings on labels:
SEDBUK 2005 – Rates boiler efficiency from A to G. A-rated boilers are above 90% efficient.
SEDBUK 2009 – This is a newer system which shows combi boiler efficiency as a percentage instead of letters. All new boilers should be rated using SEDBUK 2009, but you may still see older models which were tested under the old SEBUK 2005 system. A combi boiler which was A-rated 90% under SEDBUK 2005 will be 88% under the new SEDBUK 2009. The difference is mainly down to differences in efficiencies between using a boiler to heat a home in the winter months, and only using it for heating water in the summer. Boiler manufacturers display SEDBUK 2005 rating on their website and manuals because it gives them a higher figure for combi boiler efficiency.
The table below shows SEDBUK figures for Annual Energy Costs to heat your home for different types of Boilers:
|Type of Boiler||Efficiency||Semi-Detached||Detached||Flat|
|Modern Condensing Boiler||89%-92%||£740||£1050||£450|
|Old Back Boiler (Light Weight)||60%-65%||£1020||£1450||£670|
|Old Back Boiler (Heavy Weight)||50%-55%||£1210||£1720||£790|
Condensing Combi Boiler Reliability
If you see a website advertising a new combi boiler installation cost, for ex. “£1695 inc. VAT for a new combi boiler on your wall!” that is possibly for the easiest new combi boiler installation cost, for ex. swapping your old combi boiler with a new one. In many cases low prices may also be down to a cheaper, lower efficiency boiler with substandard parts.
Whichever boiler system you convert to combi from, below are the steps taken as standard for each installation:
- Drain existing heating & hot water system.
- Remove existing boiler, and any hot water cylinder and attic tanks.
- Controls will be upgraded to ones suitable for a combi boiler.
- Existing smart controls like Nest or Hive can be configured to work with the new combi boiler.
- All scrap to be carted away from site and recycled.
- The central heating system will be converted to combi.
- Gas run will be upgraded to 22mm pipes for modern, condensing combi boilers.
Once all of that is done, the following will be installed:
- Brand New, Modern Condensing Combination Boiler
- Horizontal or Vertical Flue
- Microbubble Deaerator [If the Client Wants it]
- Magnetic Filter
- Limescale Filter
- Boiler Plus Compliant Programmable Thermostat
- OR Internet Enabled Learning Thermostat
- North Facing Weather Compensation
- Chemical Flush & Add an Approved Inhibitor
- Associated Pipe Work to Complete Installation
- Registration of Extended 7-10 Years Warranties
- Commission & Test to MFI & Complete Benchmark
- Building Regulation Notification with Certification including Landlord Certificates
- Hand Over & Induction on Boiler, Controls & Best Usage
Below are the approximate costs for installation and conversion from different boiler setups to combi:
Cost to Convert Open Vent to New Condensing Combi Boiler
Should You Try and Install a Combi Boiler Yourself?
Please DO NOT try and install a boiler yourself.
New gas connections will have to be made, which means only Gas Safe Registered Engineers should do it. If you try to do it yourself, or get a plumber without the proper certification to do it, without the required tools, you can face heavy fine or even prison time.
Why does the UK law require you to do so?
- Gas Safe Registered Engineers spend 5 years studying, and hit their true level of experience in 5-10 years.
- Flue Gas Analysers, which cost between £600 & £1000, are required by law.
- Flues Gas Analysers need to be calibrated annually and hold a certificate.
- Suitability of the combi boiler for the property needs to be checked.
- Boiler siting needs to be safe and comply with Gas Safe & Building Regulations.
- Manufacturer specified appropriate materials and fittings have to be used.
- If you or your plumber are not Gas Safe Registered and make a new gas connection to a boiler = heavy fines or prison.
- Equipment like Manometers test the gas supply and make sure the pressures are safe.
- Gas integrity needs to be tested prior to connecting the boiler. And again once connected.
- Let-by test & tightness test.
- Flow rates need to be checked and adjusted.
- Gas Safe Engineers need to gas rate the boiler, and check gas pressures and flue integrity.
Best Combi Boilers 2019 UK – Gas/LPG
Below is a list of not only the best condensing combi boilers in the UK, but most of these are also the most energy efficient combi boilers on.
This is the most powerful and highest efficiency condensing combi boiler money can buy in the UK right now. There’s nothing else quite like it in the domestic boiler range in the UK from any of its rivals. It’s also number 1 in condensing combi boiler list in Germany.
- 98% Energy Efficiency. Almost all of the fuel used is converted into heat
- 5 inch colour touchscreen. Easy to operate Vitotronic control unit.
- Control via app and internet (with optional Vitoconnect 100 WLAN adaptor)
- High Quality Inox-Radial Stainless Steel Heat Exchanger
- Quietest boiler in the UK at only 34 decibels
- Compact dimensions, only 450 mm wide
- Optional remote fault notifications for Viessmann Trained Installers
This boiler bridges the gap between affordable combi boilers and the absolute premium.
For a full review of the 100-W, please click here.
- High Quality Stainless Steel Inox-Radial Heat Exchanger
- Backlit LCD Touch Screen for Easy Operation
- Class A rated for Energy Efficiency
- Available in outputs from 4.7 to 35 kW
- Up to 10 year extended warranty available
- LPG Conversion Kit Available
Definitely one of the best boilers available in the UK right now. It sits right between the entry level Vitodens 050-W and the high end, premium Vitodens 200-W.
This is a surprise entry on the list of best combi boilers 2019. Very few people know about ATAG in the UK. That’s because this is an unbiased list focusing mostly on technologically brilliant, energy efficient combi boilers.
- 10 Year Warranty
- Unique iCon stainless steel heat exchanger
- Instant hot water with pre-heat facility
- Built in Passive Flue Gas Heat Recovery Device
Another big German brand operating in the UK for many years, manufacturing high quality, high efficiency, robust boilers.
The Vaillant ecoTEC Plus Condensing Combi Boiler features:
- Stainless Steel Heat Exchanger
- 5-year guarantee as standard, with 7 to 10 years available when you book a Vaillant Advance installer
- Dimensions in mm (825 model): H 720 x W 440 x D 338
- Works with LPG where required
Market leader in the UK for many years, but lagging behind in terms of technology, especially quality of internal components as the company has chosen to stick with aluminium.
Some features of their flagship Greenstar CDi range:
- Simple boiler control knobs with clear temperature display
- Larger two bathroom properties can be supplied by higher output options
- Wide choice of controls enables greater comfort and economy
- Instantaneous hot water, always available
Winner of the Which? Best Buy Award for the second year running in 2018, this condensing combi boiler is comparable to the Worcester Bosch and Vaillant models, but cheaper.
- Ultra Compact – Just 707mm in height
- DHW output ratings of 5.9 to 35 kW
- High quality stainless steel Inox-Radial heat exchanger
- High efficiency – up to 97% (Hs) [gross cv]
Worcester Bosch’s more affordable boiler. This is in the price range of the Viessmann Vitodens 050-w which is one place higher on this list of best combi boilers 2019. In some cases it’s more expensive than the 050-w, which is crazy considering this is a lower quality boiler with an aluminium heat exchanger.
- Wide choice of controls enables greater comfort and economy
- Low energy pump reduces electrical usage
- Hot water instantly heated from cold mains
Buy a Combi Boiler Online
Who Should You Buy a Combi Boiler from?
It’s probably a good idea to look for online reviews. But be careful as a lot of online “review collector” companies have popped up recently. To our knowledge, two of the best review websites are Trustpilot and FreeIndex.
Every review is verified by Trustpilot, and they won’t allow a company to remove negative reviews. A negative review can be reported by a company, and Trustpilot will investigate with the customer before taking any action.
Get an Online Boiler Quote
We provide free, no-obligation online quotes for a condensing combi boiler, which takes only a few minutes. Try it now by putting your postcode and hitting the green button below: