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Choosing a new Combi Boiler

In this page we will first show you how to determine the requirements for your hot water and heatings needs. Then we will proceed to choosing different brands. If you would like to know the different boiler types then see Boiler Types. Approximately 74% to 80% of uk properties contain a combi boiler. A combi boiler is simply an boiler capable of producing instantaneous water and heating. The disadvantage of a combi boiler is that potentially if the boiler breaks you can lose both heating and hot water. There is no immersion backup like regular/system boilers with hot water cylinder. The workaround to this is to also install one electric shower. The tradeoff is between a space saving instant hot water and a space occupying higher performance boiler with cylinder with immersion backup.  For this article we will proceed to assume that you have accepted the tradeoffs of a combi boiler.  We will also assume that you require heating for radiators and/or underfloor heating.

Hot water requirements

Assumptions for calculations
– you require heating for radiators and/or underfloor heating.
– temperature rise is based on 35 degrees celcius

Choosing a brand of boiler

In our opinion having installed a variety of boilers. We have selected the top 7 brands that are commonly used and are considered to be the more reliable boilers on average, although things can change on a frequent basis. Each brand may have differences in terms of certain features. We will list this in a separate article in detail. However important features are listed in the table below, next to each brand.

Top Brands :

BrandMarket Share(Annual)*Guarantee rangeOpenThermUnique attributesPrice LevelQuality
AtagSmall10 YearsYesSolid Stainless Steel Heat exchangerHighHigh
BaxiSmallUpto 10 yearsYes (Selected Models)MediumMedium
Glowworm (Part of Vaillant Group)MediumUpto 15 yearsNoMediumMedium
Ideal High (Approx 25%), 415 K Boilers a year. Upto 12 YearsYesSimple Design, UK ManufacturingMediumMedium
IntergasSmall3- 10 YearsYesUnique 2 in 1 heat exchanger, 4 moving parts.MediumHigh
Main (Part of Baxi Group)MediumUpto 5 YearsYes (Selected Models)LowMedium
Potterton (Part of Baxi Group)MediumMediumMedium
VaillantHigh(Approx 20%-23%)Upto 10 YearsNoHighHigh
ViessmannMediumUpto 10 YearsYes (limited support)Large bore stainless steel inox heat exchanger.HighHigh
Worcester BoschHigh (Approx 30%) 490K Boilers a year.Upto 10 YearsNoLarge customer call center. Royal CharterHighHigh

Other Considerations

As no house is usually identical to one another, choosing a combi boiler is not always straight forward. Even in supposed identical new builds, variations exist, due to tradesman and stakeholders doing things not according to plan. We have listed the most important considerations when choosing a new combi boiler. These several factors will decide which boiler you should go with.

Engineer preference: Choosing a boiler based on engineers and their expertise. This is probably the most important consideration rather the the product itself. There may not be a specialist in some of the brands listed near you, therefore you are limited to the engineers that are available in your area. At the end of the day, your boiler will require annual servicing and ongoing future support. So have access to engineers with the expertise for your particular boiler is crucial for the long term

Suitability: A Combi boiler may not always be suitable or recommended for particular properties. Some people’s kitchen cupboards may not have the area available for bigger boilers. Flue routing may restrict your choice to certain boiler models.

Warranty / Guarantee: Boiler brands have varying warranty from the statutory 1 year upto 15 years. You will tend to pay a higher premium for boilers with longer warranty. Also these warranties require annual maintenance / servicing to be carried out. Remember, some smaller manufacturers may offer larger warranties, however their support may be stretched at critical times such as winter. So choosing based on support levels as well as warranty length may be the way to go.

OpenTherm support: This is considered important in our opinion and for the future. It is an interface on the boiler that allows two way communication between compatible controls in order to achieve true modulation. Opentherm is universal interface that can allow the likes of a Nest Thermostat, Honeywell Lyric or other opentherm thermostat to talk to the boiler. See What is OpenTherm, and OpenTherm capable boilers Article.

Availability: Some of these boiler brands may not be easily available in your area from local merchants. You may require internet ordering or special ordering. Likewise, this also applies to parts availability for when your boiler is out of warranty. In some cases, part availability may be even harder from local merchants, and only available as special order or through internet retailers.

Gas supply: Bigger combi boilers require larger gas supplies depending on distance from the meter. If your existing pipe is concealed and there is no way to run a new pipe without it being visible, you may be restricted as to what size combi boiler you can go with. So the closer the boiler is to the gas meter, the more likely you are able to go for a larger combi.

Water supply: As well as a larger gas supply, bigger combi boilers require higher water flow rates. If you have an older lead pipe, or small supply, you may have to have this upgraded to accomodate the higher flow rates. As a guideline, the water supply companies are required to legally supply 9 liters a min, with 1 bar minimum pressure. Running a new water supply could be simple or complex depending on your properties arrangements and existing supply.

Disclaimer: Information on this website is provided for informational purpose therefore we cannot accept liability for subsequent problems. All repair tasks should be carried out by qualified trades people. We may also receive commission payments when you are taken to external websites and complete purchases from third party sellers, once you leave our site, we cannot be held liable for your purchases.