Combi Boiler Installation

Combi boiler installation across the UK

If you are looking for a combi boiler installation, we are here to provide you with that. At Boilerhut, we have a large network of combi boiler installers who supply and install gas oil and LPG combi boilers to postcodes across the UK.

A combi boiler installation is usually a straightforward affair, but it requires expert installation and a qualified engineer. All of our engineers are Gas Safe Registered, OFTEC Registered and have oil and LPG certifications, enabling them to install gas, oil and LPG boilers.

Looking for a combi boiler installation?

The most popular type of boiler in the UK

Combination boilers – more commonly known as combi boilers, are the most popular type of boiler sold in the UK for central heating and domestic hot water.

Whilst first produced by Vaillant in the early 1960s and introduced to the UK by Worcester in 1971, combi boilers have gained massive popularity over the past 20 years or so, due to the excellent efficiency and heating capabilities they now provide. As they are compact, require no hot water cylinder or cold water tanks, over 70% of UK households now choose these over other boiler types.

Even if you have a larger property, there are still combi boiler options available for you.

Cost Calculation

How much does combi boiler installation cost?

The cost to install a combi boiler will vary depending on the boiler that it is replacing.

Below we have illustrated various installation scenarios and have detailed the typical costs for installing a new combi boiler in the same location and for installing a new combi boiler in a new location. It should be noted that the cost for moving the boiler will vary according to where it is moved to.

Combi BoilerReplacing an existing combi boiler with a new combi boiler

A combi to combi boiler swap is the easiest and the quickest combi boiler installation as it is replacing like for like. Below, we have detailed the average costs and installation time for this type of installation.

Type of installation Average cost Installation time  
Replacing an existing combi boiler with a new boiler, in the same location £2000 – £2500 1 day
Replacing an existing combi boiler with a new boiler, in a new location £2500-£3000 1 to 2 days
Looking to replace your existing combi boiler with a new combi boiler?

System BoilerReplacing a regular/system boiler and a hot water cylinder with a combi boiler

Regular boilers are fed by two header tanks in the loft, an external pump is used to pump water around the radiators and hot water is stored in a cylinder. A combi boiler will replace all of these components. Below, we have provided the average cost and installation time to remove the hot water cylinder and redirect the hot water pipes to the new combi boiler location.

Type of installation Average cost Installation time  
Replacing an existing regular boiler and hot water tank with a new combi boiler* £2,900 2 days
Looking to replace your existing regular/system boiler and a hot water cylinder with a new combi boiler?

back boiler conversion to combi boiler installationReplacing a back boiler with a combi boiler 

Back boilers are a type of conventional boiler which were installed in open fireplaces in residential properties from the 1960s. They were phased out in 2005 when the new high-efficiency regulations were implemented, making it very difficult and expensive to fit this type of boiler. Providing central heating and domestic hot water, due to their high build quality and simplicity it is not uncommon for them to still be running today.

The main reason to swap a back boiler with a combi boiler is due to low efficiency, replacing a back boiler for a combi boiler could save you £300-£500 on your annual gas bill.

Below, we have provided the average cost and installation time for removing the back boiler and the hot water cylinder and replacing it with a combi boiler.

Type of installation Average cost Installation time  
Replacing a back boiler and hot water tank with a new combi boiler £3500 2/3 days
Looking to replace your existing back boiler with a new combi boiler?
What is an LPG Combi Boiler?

What is a combi boiler?

Combi boilers are a space-saving boiler type that house all of the water heating and central heating components in one compact unit.

Heating directly from the mains, a combi boiler will provide you with an unlimited supply of instant hot water when you turn on a tap or shower. This water is delivered through your pipes at mains pressure where it arrives at your taps and showers.

Combi boilers only heat water when a hot tap or shower is turned on, this ensures maximum efficiency and means that it won’t cost you anything until this is used. To allow for quick delivery of hot water, the length of the pipe run from the boiler to the furthest outlet should be considered.

The central heating portion of a combi boiler is on a pressurised closed loop system, heated by the boiler as required. 

If you are short on space or you are looking to better utilise areas of your home, a combi boiler will be ideal because there is no need for a cold water tank in the loft nor a hot water cylinder in the airing cupboard.

Combi boilers deliver hot water through your taps or showers at mains pressure. This means that if your mains water pressure is good enough, you can enjoy hot showers without needing any extra pumps.

As no hot water is stored in an external cylinder and it is delivered as and when required, combi boilers are designed to maximise the amount of energy that is directly used to heat the water. This means there is no need to heat up and store more water than is required, reducing your carbon footprint and cutting down your energy bills.

Combi boilers are straightforward to install, economical to run and are typically installed in a kitchen, utility or airing cupboard. Flueing options should be considered when locating a new boiler (horizontal or vertical).

Gas Combi Boilers

How does a combi boiler work?

Whether your combi boiler runs on mains gas, oil or LPG, the fuel enters a sealed combustion chamber inside the boiler and an electric ignition sets it alight. The primary heat exchanger within the boiler then heats incoming water up to the required temperature, which then flows through all of the radiators in your home or is delivered to taps and showers, as needed.

Combi boilers have two heat exchangers inside them:

  1. A primary heat exchanger (for central heating and hot water)
  2. A secondary plate heat exchanger (for hot water)

The primary heat exchanger heats and recycles the water that goes through the pipes into the radiators.

The secondary plate heat exchanger uses that returning hot water from radiators, and heats up sealed pipes with potable water that goes into your taps.

Our guide will provide more detail about how a combi boiler works – How Does a Combi Boiler Work?

how a combi boiler works

Is a combi boiler suitable for my house?

The compact size of combi boilers makes them an ideal choice for properties with limited space. Combi boilers are not just a solution for flats and smaller houses though, combi boilers come in a variety of outputs making them suitable for properties of a range of sizes.

For instance, modern combi boilers now exist which are equipped to deal with the hot water and heating requirements of homes with 4+ bedrooms, 2+ bathrooms and 20+ radiators. Called storage combi boilers, these larger combi boilers house a thermal water storage tank within the unit itself. An example of one of these boilers is the Viessmann 111-W Storage Combi, which houses a 46-litre stainless steel thermal store within the boiler itself. This is a great option because even if you call for hot water in two bathrooms, you will still get it at mains pressure.

Generally, the larger the house and the higher the hot water demands, the higher the kilowatt rating the boiler should be. To illustrate this, we have matched combi boiler outputs to the property size that they are suitable for.

Combi Boiler kW Output Property Suitability
24-27kW Properties with 1-2 bedrooms, 10 radiators and 1 bathroom
28-34kW Properties with 3-4 bedrooms, 15 radiators and 1-2 bathrooms
35-42kW Properties with 4+ bedrooms, 20 radiators and 2+ bathrooms
It is worth considering the following too:

How much hot water do you use?

Hot Water Usage

If you require hot water from multiple taps at the same time, including showers, then perhaps a regular combi boiler won’t be enough. However, for properties with higher hot water demands, a storage combi boiler will be able to handle the hot water demands from several taps at once.

In the case of the Viessmann Vitodens 111-W, it utilises an integrated stainless steel thermal store with CLS (cylinder loading system). This makes sure that it refills the in-built thermal store within a few seconds without affecting the final flow rate. The Viessmann Vitodens 111-W can handle up to three bathrooms.

However, if you live in a larger house, it may be that a combi boiler isn’t the right option for you and you may want to consider a conventional boiler or a system boiler with an external hot water cylinder instead.

How close will the combi boiler be to the bathroom?

How close will the combi boiler be to the bathroom?

If you are planning to install your new combi boiler in the garage and you have a bathroom on the other side of the house, you could experience a delay in the time it takes for water to heat up and reach your taps and showers. For best results, your combi boiler should either be installed reasonably close to your bathroom, or equidistant to the kitchen taps and bathroom.

Advantages and disadvantages of combi boilers

Combi boiler advantages

  • Compact in size, meaning you have more options for where the boiler can be positioned in the property 
  • No need for a separate cold water tank or hot water cylinder ensures space in your property is saved and means there are fewer things to go wrong
  • Hot water on demand – instant and unlimited hot water that is provided as and when required
  • Energy bills are lowered – because of the way that hot water is supplied, no waste is created from unnecessarily heated water
  • Cheaper to install than system and conventional boilers as there is less pipework and components
  • No issues with air locks or low pressure as hot water is taken directly from the water mains

Combi boiler disadvantages

  • Combi boilers require good mains water pressure to operate properly 
  • Not suitable for use with power showers
  • As all components are combined, you will be left without heating and hot water if your combi boiler breaks down
  • If your house has too many bathrooms, a combi boiler may not be able to provide on-demand hot water to all of them simultaneously
Looking for combi boiler installation?

Points to consider when getting a combi boiler installed 

Do you have a 22mm gas supply?

All modern combi boilers require a 22mm gas supply. To determine whether you already have this, you will need to look at the gas supply pipe used for your current boiler. This is usually below the boiler to the middle, look for a yellow tap to identify where this is.

Gas Pipes

Where will your condensate pipe go?

Combi boilers need to emit condensate into an internal water waste pipe or an external drain or soakaway

Plume kit

This example shows a plume kit taking the flue away from an opening or a window, as per building regulations.

Flue position

Building regulations and Gas Safe requirements state that all flues need to be 300mm to 600mm away from a window opening

Combi boilers are available from many boiler manufacturers operating in the UK. Below, you will find an overview of some of the most popular combi boiler brands available in the UK. 

Brand About the brand
Alpha

Alpha Boilers

Italian brand Alpha has been offering boilers to the UK market for over 50 years. 

Typical warranty period: Up to a 13-year warranty

Notable technology: Stainless steel heat exchangers

Fuel types: Gas

Outputs: 28 to 38kW

Country of manufacture: Italy

Combi Boiler Range Kilowatt (kW) Outputs
E-Tec Plus 28, 33, 38
E-Tec 28, 33
Evoke 28, 33
Ariston

Ariston

Ariston has been producing boilers since 1980, manufacturing its combi boiler range at its production facility in Italy. 

Typical warranty period: Up to a 12-year warranty

Notable technology: Patented Xtratech™ stainless steel heat exchangers

Fuel types: Gas and LPG

Outputs: 24 to 38kW

Country of manufacture: Italy

Combi Boiler Range Kilowatt (kW) Outputs
Alteas ONE Net 30, 35
Genus ONE Net 24, 30, 35
Clas ONE 24, 30, 38
E-Combi ONE 24, 30
E-Combi ONE LPG 24, 30
Atag

ATAG

Founded in The Netherlands, ATAG has been designing and manufacturing boilers for almost 70 years. 

Typical warranty period: Up to a 14-year warranty on the boiler, lifetime guarantee on the heat exchanger

Notable technology: iCon stainless steel heat exchanger

Fuel types: Gas

Outputs: 24 to 40kW

Country of manufacture: The Netherlands

Combi Boiler Range Kilowatt (kW) Outputs
iC Combination 24, 28, 36, 40
Baxi

Baxi

Baxi has been manufacturing heating systems in the UK since 1866. 

Typical warranty period: Up to a 10-year warranty on the boiler, lifetime guarantee on the heat exchanger

Notable technology: Aluminium heat exchangers, brass components

Fuel types: Gas and LPG

Outputs: 24 to 40kW

Country of manufacture: The UK

Combi Boiler Range Kilowatt (kW) Outputs
200 Combi 24, 28
400 Combi 24, 28
600 Combi 24, 30, 36
800 Combi 25, 30, 36
636 Combi LPG 36
Duo-tec Combi 24, 28, 33, 40
Platinum Combi 24, 28, 33, 40
Platinum+ 40kW Combi 40
400 Combi LPG 28
600 Combi LPG 24, 30, 36
Duo-tec Combi LPG 28
Biasi 

Manufacturing domestic boilers in Italy since the 1940s, Biasi has been providing combi boilers to the UK market since 1990.

The current Biasi combi boiler range comprises the Advance Plus 7 Combi and the Advance Combi.

Biasi’s combi boiler range is available in outputs from 25kW to 35kW, features stainless steel heat exchangers, and comes with up to a five-year warranty.

Biasi offers gas and LPG combi boilers.

Combi Boiler Range Kilowatt (kW) Outputs
Advance Plus 7 25, 30, 35
Advance Combi 25, 30, 35
Ferroli 

Ferroli

Founded in Italy in 1955, Ferroli has been providing combi boilers to the UK market since 1988.

Ferroli’s current combi boiler range, called Bluehelix Tech RRT, comprises boilers available in outputs from 24.5kW to 34kW, features stainless steel heat exchangers, and come with a 10 year warranty. 

Ferroli offers gas combi boilers.

Combi Boiler Range Kilowatt (kW) Outputs
Bluehelix Tech RRT 24, 28, 34
Glow-worm

Glow-worm

Glow-worm has been producing boilers for the UK market at its production facilities in Derbyshire since 1934.

Glow-worm currently offers combi boilers across three ranges – Betacom₄, Ultimate₃, Easicom₃, Essential, Energy LPG and Energy 35 Store combi boilers.

Across its boiler ranges, Glow-worm offers combi boilers in outputs from 24kW to 35kW. Glow-worm combi boilers feature aluminium heat exchangers and come with up to a 5-year warranty.

Glow-worm offers gas and LPG boilers.

Combi Boiler Range Kilowatt (kW) Outputs
Energy 25, 30, 35
Energy 35 Store 35
Ultimate₃ 30, 35
Betacom₄ 24, 30
Easicom₃ 24, 28
Essential 24, 28
Energy LPG 30
Grant

Grant

Grant specialise in oil combi boilers and have been providing boilers to the UK market since 1970.

Grant currently offers oil combi boilers across the Vortex Blue, Vortex Pro and Vortex Eco ranges.

Grant’s oil combi boilers are available in outputs from 21kW to 35kW, feature stainless steel heat exchangers, market-leading Riello Blue Flame burners, and come with up to a 10-year guarantee.

Grant offers oil combi boilers.

Combi Boiler Range Kilowatt (kW) Outputs
Vortex Blue 21, 26, 36
Vortex Pro 21, 26, 36, 46, 58, 70
Vortex Eco 21, 26, 35
Ideal

Ideal Heating

Ideal has been providing boilers to the UK market since 1906.

The current Ideal boiler offering comprises the Logic Max Combi, Vogue Max Combi, Vogue Gen2 Combi and Logic+ Combi ranges.

Ideal combi boilers are available in outputs from 26kW to 40kW, feature aluminium heat exchangers, and come with up to a 12-year warranty.

Ideal offers gas and LPG combi boilers.

Combi Boiler Range Kilowatt (kW) Outputs
Logic Max Combi 24, 30, 35
Vogue Max Combi 26, 32, 40
Vogue Gen2 Combi 26, 32, 40
Logic+ Combi 24, 30, 35
Intergas

Intergas are a Dutch boiler manufacturer that has been manufacturing boilers for over 50 years.

The current combi boilers available from Intergas consists of the Xtreme, HRE, Xclusive, ECO RF and Rapid ranges.

Intergas combi boilers are available in outputs from 17kW to 41kW, feature aluminium heat exchangers, and come with up to a 10-year warranty. 

Intergas offers gas and LPG combi boilers.

Combi Boiler Range Kilowatt (kW) Outputs
Xtreme 24, 30, 36
HRE 17, 23, 27, 41
Xclusive 24, 30, 36
ECO RF 18, 23, 27
Rapid 25, 32
Navien

Navien

Navien is a South Korean boiler manufacturer that was founded in 1978 and has been providing boilers to the UK market since 2014.

Navien’s current combi boilers comprise the NCB and LCB700 ranges.

Navien’s combi boilers are available in both oil and gas, come in outputs from 24kW to 40kW, feature stainless steel heat exchangers, and come with up to a 10 year warranty.

Navien offers gas and oil combi boilers.

Combi Boiler Range Kilowatt (kW) Outputs
NCB 24, 28, 34, 40
LCB700 21, 28, 36
Vaillant

Vaillant

Founded in Germany in 1874, Vaillant has been offering boilers to the UK market since the 1970s.

Vaillant’s currently offers the ecoTEC exclusive, ecoTEC plus, ecoTEC plus combi store, ecoTEC pro and ecoFIT pure combi boiler ranges.

Recipients of multiple Which? Best Buy awards, Vaillant combi boilers are available in outputs of 24kW to 43kW, feature a stainless steel heat exchanger, and come with up to a 10-year guarantee.

Combi Boiler Range Kilowatt (kW) Outputs
ecoTEC exclusive 35, 43
ecoTEC plus 25, 32, 35, 38
ecoTEC plus combi store 38
ecoTEC pro 24, 28, 30
ecoFIT pure 25, 30, 35
Viessmann

Viessmann

Founded in Germany in 1917, Viessmann has been offering combi boilers to the UK market since 1989. 

Viessmann’s current combi boiler range comprises the Vitodens 050-W, Vitodens 100-W, Vitodens 111-W, Vitodens 200-W and the Vitodens 222-F.

Recipients of multiple Which? Best Buy awards, Viessmann combi boilers are available in outputs from 26kW to 35kW, feature stainless steel Inox-Radial heat exchangers, and come with up to a 12-year warranty.

Viessmann offers gas and LPG combi boilers.

Combi Boiler Range Kilowatt (kW) Outputs
Vitodens 050-W 29, 35
Vitodens 100-W 26, 30, 32
Vitodens 111-W 25, 32
Vitodens 200-W 30, 35
Worcester Bosch

Worcester Bosch Group

Worcester Bosch was originally founded as Worcester in 1962, before becoming part of the Bosch Group in 1996 and becoming Worcester Bosch. 

Currently, the UK market leader for domestic boilers, all of their combi boilers are assembled at their UK production facility in Worcester. 

Recipients of multiple Which? Best Buy awards, Worcester Bosch’s Lifestyle and Greenstar combi boiler ranges are available in outputs from 24kW to 50kW, feature aluminium heat exchangers, and come with up to a 12-year warranty.

Worcester Bosch offers gas, LPG and oil combi boilers.

Combi Boiler Range Kilowatt (kW) Outputs
Greenstar 8000 Life Combi 30, 35, 40, 45
Greenstar 8000 Style Combi 30, 35, 40, 45
Greenstar i 25, 30
Greenstar Si Compact 25, 30
Greenstar CDi Compact 28, 32, 36
Greenstar CDi Highflow 29, 31
Greenstar Heatslave II 18, 25, 32
Greenstar Heatslave II External 18, 25, 32
Greenstar 2000 25, 30
Greenstar 4000 25, 30

Popular gas combi boilers

Viessmann Vitodens 0-50-W Gas Combi Boiler

Viessmann-Vitodens-050-W

Ariston Clas ONE Gas Combi Boiler


Ariston CLAS One

Worcester Bosch Greenstar 8000 Gas Combi Boiler

Worcester Bosch Greenstar 8000

Looking for gas combi boiler installation?

Popular oil combi boilers

Worcester Bosch Greenstar Heatslave II Oil Combi Boiler

Worcester Greenstar Heatslave II Combi

Navien LCB700 Blue Flame Oil Boiler

Navien LCB700
Looking for oil combi boiler installation?

Popular LPG combi boilers

Viessmann Vitodens 200-W Gas Combi Boiler

Viessmann Vitodens 200-W

Worcester Bosch Greenstar CDi Compact Gas Combi Boiler

Worcester Bosch Greenstar CDi Compact Combi
Looking for LPG combi boiler installation?