Converting a Back Boiler to a Combi Boiler in Liverpool: A Step-by-Step Guide
- Sep 26, 2023
- 14 min read
Updated: 2 days ago
Last updated: March 2026. This guide has been fully revised to include an expanded step-by-step conversion process, Vaillant ecoTEC-exclusive Green iQ product information, updated costs, and a new FAQ section.
ecoTEC exclusive with Green iQ
The premium combi boiler
The best in boiler performance, control and efficiency for specifiers
Fully compatible with our vSMART™ heating control for optimum performance and smartphone app control for the occupier
Eco-friendly and 85% recyclable
Hand-assembled in our award-winning Derbyshire manufacturing plant
If your home still has a back boiler tucked behind the fireplace, you are not alone. Thousands of properties across Liverpool, Wirral, and the wider Merseyside area were built or fitted with back boilers during the 1960s, 70s, and 80s, and many are still in operation today. While these systems did the job for decades, a back boiler conversion to a modern combi boiler is one of the most impactful home improvements you can make, both for your comfort and your energy bills.
This guide covers everything you need to know: why back boilers are being phased out, what the conversion process actually involves, how long it takes, what it costs, and how to choose the right boiler for your home. We have also included a detailed look at one of our most popular upgrade options, the Vaillant ecoTEC exclusive with Green iQ, and a step-by-step breakdown of how DD Wilson handles every conversion from start to finish.
What Is a Back Boiler and Why Are They Still in Liverpool Homes?
A back boiler is a heating unit installed inside a fireplace cavity, typically behind a gas fire or decorative surround. It heats water for your radiators and hot-water taps by burning gas in a compact unit concealed behind the chimney breast. The system usually works alongside a separate hot water cylinder in the airing cupboard and a cold water tank in the loft, which means three separate components doing the work a single modern boiler now handles alone.
Liverpool's housing stock, particularly the terraced and semi-detached properties in areas such as Wavertree, Bootle, Kirkby, Crosby, and Huyton, features a high proportion of back-boiler installations simply because those homes were built at a time when back-boiler installations were common. Many were installed correctly for their era and have limped along for 30 or even 40 years, which is remarkable, but also a sign that a conversion is well overdue.
Back boilers are no longer manufactured in the UK. Spare parts are increasingly difficult to source, and any heating engineer who services one will tell you the same thing: getting a replacement part is becoming harder every year. If your back boiler develops a serious fault, you may be looking at a forced emergency replacement with very little time to plan. Understanding how long boilers last and planning ahead is always the smarter approach.
Why Are Homeowners Replacing Back Boilers?
The reasons to convert a back boiler to a combi are both practical and financial. Here are the main drivers we hear from homeowners across Merseyside and South Lancashire.
Energy Efficiency
Old back boilers typically operate at around 60 to 70 per cent efficiency, which means up to 30 to 40 pence in every pound spent on gas is lost up the flue. A modern A-rated combi boiler operates at 92 per cent efficiency or higher. That gap translates directly into lower gas bills, often saving Liverpool households several hundred pounds per year. Our boiler efficiency guide for Merseyside homeowners explains this in more detail.
Space
Replacing a back boiler system typically means removing the gas fire, the fireplace surround, the hot water cylinder in the airing cupboard, and the cold water tank in the loft. A combi boiler is a single wall-hung unit, usually no larger than a kitchen cupboard, which frees up considerable storage and living space.
Hot Water on Demand
A combi boiler heats water directly from the mains as it flows through the unit, which means you get instant hot water at the tap without waiting for a cylinder to heat up. There is no risk of running out of hot water mid-shower, and you only heat what you actually use.
Reliability and Parts Availability
As noted above, back boiler components are becoming obsolete. A conversion now, on your own terms and timeline, is far better than a breakdown in January, forcing an emergency replacement at short notice. Our team handles boiler repair services across Liverpool daily, and we see the consequences of delayed action regularly.
Environmental Impact
Reducing gas consumption directly reduces carbon emissions. Upgrading to a high-efficiency combi boiler is a straightforward step towards a greener home and, with hydrogen-blend ready boilers now available, it also positions your heating system for the future.
Choosing the Right Combi Boiler for Your Home
Not all combi boilers are equal. Output size, brand reliability, controls compatibility, and warranty terms all vary significantly. For homes in Liverpool and the surrounding area, we work with several market-leading manufacturers, and our most recommended premium option for back boiler conversions is the Vaillant ecoTEC exclusive with Green iQ. We always advise homeowners to read our guide to choosing the right boiler for homes in Merseyside, Cheshire, and Lancashire before committing to a model.
Spotlight: Vaillant ecoTEC Exclusive with Green iQ
The Vaillant ecoTEC exclusive with Green iQ is Vaillant's flagship combi boiler, hand-assembled at their award-winning manufacturing plant in Belper, Derbyshire. It is designed for specifiers and homeowners who want the best available in performance, control, and efficiency rather than the cheapest option on the market.
DD Wilson is a Vaillant Advance Master Tech installer, which means our engineers receive manufacturer training directly from Vaillant and are qualified to install and commission their full product range to the highest standard. This matters because premium boilers only deliver their full potential when installed and set up correctly.
Key features of the ecoTEC exclusive with Green iQ include:
Performance and efficiency leadership: The ecoTEC exclusive with Green iQ is the top of Vaillant's combi range for output efficiency, making it the choice of heating specifiers who need to demonstrate energy performance credentials to clients or building regulations assessors.
vSMART heating control compatibility: The boiler is fully compatible with Vaillant's vSMART system, which offers smartphone app control for homeowners. You can adjust your heating schedule, set temperature zones, and monitor usage from anywhere. This is the kind of control that makes a genuine difference to energy consumption when used properly, rather than smart technology for its own sake.
Eco-friendly manufacture: The ecoTEC exclusive with Green iQ is 85 per cent recyclable by material, supporting Vaillant's broader sustainability commitments and contributing to environmental credentials that are increasingly relevant to landlords, housing associations, and homeowners seeking EPC improvements.
UK manufacturing: Every unit is hand-assembled at Vaillant's Belper facility in Derbyshire, ensuring quality control standards align with its extended warranty commitments.
When you book a boiler installation with DD Wilson, we carry out a full pre-survey to establish the correct output size for your property, the best location for the new boiler, and whether the ecoTEC exclusive or another model within Vaillant's range or the ATAG portfolio suits your specific requirements. You can also see what previous customers have said about their Vaillant boiler installation experience with DD Wilson.
The Back Boiler to Combi Conversion: Step by Step
A back boiler conversion is more involved than a straightforward combi-to-combi swap. It requires removing an entire heating system and replacing it with a fundamentally different configuration. Here is how our engineers approach each job.
Step 1: Pre-Installation Survey
Before any work begins, a DD Wilson engineer visits your property to assess the existing system: the back boiler model and condition, the flue route, the radiator layout, the pipework size, the mains water pressure, and the loft access. This survey informs the quotation and identifies any complications in advance so there are no surprises on installation day. Our guide to understanding the timeline for standard and complex boiler installations gives a clear picture of what to expect.
Step 2: Isolating and Decommissioning the Back Boiler
On installation day, the engineer isolates the gas supply to the back boiler and the water supply to the existing cylinder and cold water tank. The system is drained down before any removal work begins. All decommissioning is carried out by a Gas Safe Registered engineer in accordance with current regulations. DD Wilson is Gas Safe Registered under number 583586, which you can verify directly on the Gas Safe Register website.
Step 3: Removing the Back Boiler and Associated Equipment
The back boiler unit is disconnected and removed from the fireplace cavity. In most Liverpool terraced and semi-detached properties, this also means removing the gas fire surround, capping off the old flue liner, and making good the chimney breast. The hot water cylinder in the airing cupboard and the cold water tank in the loft are also decommissioned and removed at this stage. This is a substantial amount of work that a straightforward boiler swap simply does not involve.
Step 4: Selecting and Installing the New Combi Boiler
The new combi boiler is positioned in the agreed location, most commonly in the kitchen, utility room, or a purpose-built cupboard. It is wall-mounted, secured to the structure, and connected to the gas supply. The flue route for the new boiler is also planned and installed at this stage; a combi boiler typically requires a horizontal flue through an external wall, which is a clean and straightforward installation in most Liverpool properties. Visit our new gas boiler installation page for more details on the range of boilers we supply and fit.
Step 5: Pipework Modifications and Connections
Because a combi boiler operates as a sealed system rather than an open vented system, the existing pipework often requires modifications. The feed and expansion tank connections are removed, and the system is converted to sealed operation with a proper expansion vessel and pressure relief valve. Existing pipe runs to radiators are assessed and upgraded where undersized. Any general plumbing issues identified during the survey, such as old or corroded pipework, are addressed at this stage.
Step 6: Radiator Assessment and Upgrades
Older back-boiler systems often fed undersized radiators that were just about keeping up with the original system's lower efficiency. With a higher-output combi boiler in place, it is worth assessing whether your radiators are correctly sized for each room. Our engineers can advise on new radiator installations where required and carry out a basic heat-loss calculation to ensure the system is properly balanced. A full central heating upgrade at the same time as the back boiler conversion makes sense for many Liverpool homeowners whose systems are decades old throughout.
Step 7: Power Flushing the System
This step is non-negotiable. Before the new boiler is commissioned, the heating system must be flushed to remove sludge, rust, and debris that accumulate in older systems. Connecting a new boiler to a contaminated system will reduce its efficiency, cause premature component failure, and in some cases void the manufacturer's warranty. DD Wilson includes a magnetic filter installation with our boiler conversions, and we strongly recommend a full power flush for any system that has been in operation for more than ten years. Our blog post on power flushing and MagnaClean filter maintenance explains the process in detail.
Step 8: System Commissioning, Testing, and Handover
Once the installation is complete, the engineer commissions the boiler in line with the manufacturer's requirements, checks for gas and water leaks, tests all radiators and controls, sets the programmer or smart thermostat, and verifies the flue seal. A Gas Safe Building Regulations notification is submitted where required. Finally, the engineer walks you through operating the new system, explains the controls, registers the warranty, and leaves you with all relevant documentation. The entire property is left clean and tidy.
What Happens to the Fireplace After a Back Boiler Removal?
This is a question we hear regularly. Once the back boiler is removed, you have several options. Many homeowners choose to brick up or board over the fireplace opening and redecorate, reclaiming the chimney breast as a feature wall. Others install a decorative electric fire in the existing recess to maintain the aesthetic without the gas connection. Some choose to have the chimney lined and install a wood-burning stove, though this involves separate building regulations work and a HETAS-registered installer. Your DD Wilson engineer can advise on what is structurally straightforward based on the specific fireplace in your property.
How Long Does a Back Boiler-to-Combi Conversion Take?
A standard back boiler conversion in a typical Liverpool terraced or semi-detached property takes two to three days for our two-person team. Day one typically covers decommissioning the old system, removing the back boiler and associated equipment, and beginning the installation of the new boiler. Day two completes the pipework modifications, connects the radiators, installs the flue, and carries out the power flush. Day three, where needed, covers final commissioning, controls programming, and any making-good work to the wall or fireplace area.
More complex properties, larger houses with multiple floors, or systems requiring significant pipework upgrades may take longer. Properties across our coverage area, from Southport to Runcorn and Chester, are handled by the same DD Wilson team, maintaining consistent standards regardless of location.
How Much Does a Back Boiler-to-Combi Conversion Cost in Liverpool?
Back boiler conversions are more expensive than like-for-like boiler replacements because of the additional labour involved in removing the old system and converting the pipework configuration. As a general guide, a back boiler conversion in a standard Liverpool terraced or semi-detached property typically starts from around £2,200 to £2,800 for a mid-range combi boiler, rising to £3,500 or more for premium models such as the Vaillant ecoTEC exclusive with Green iQ when the full conversion, power flush, and controls are included.
These figures will vary based on property size, system condition, the boiler model specified, and the extent of any pipework or radiator work required. The only accurate way to get a price for your specific property is to request a no-obligation survey. Use our quick quote tool to get started, or book a survey online directly.
It is worth checking our current best boiler deals and DD Wilson heating promotions, which regularly include package offers on back boiler conversions, particularly in the spring and autumn when demand allows more flexibility on pricing.
Finance Options and Government Schemes
The upfront cost of a back boiler conversion need not be a barrier. DD Wilson offers flexible finance options that allow you to spread the cost over a period that suits your budget, subject to status. Our financing guide explains the options in plain terms.
Depending on your circumstances, you may also be eligible for support through the government's Boiler Upgrade Scheme or other energy efficiency programmes. Our government-backed scheme page covers eligibility criteria and how to apply. Landlords and homeowners in lower-rated EPC properties can sometimes access grant funding for heating upgrades, so it is worth checking before committing to a self-funded installation.
Does My Home Have Enough Mains Pressure for a Combi Boiler?
This is an important practical consideration, particularly for older properties in parts of Liverpool, Wirral, and Merseyside where mains pressure has historically been lower. A combi boiler relies on adequate mains water pressure to deliver a satisfactory flow rate at hot taps and showers. Our pre-installation survey includes a mains pressure check, and if pressure is borderline, we will discuss your options honestly. In some cases, where mains pressure is genuinely insufficient for a combi, an unvented cylinder system may be a better solution, delivering mains-pressure hot water without relying entirely on the incoming supply rate. We also supply and install hot water cylinders where a stored hot water solution better suits the property.
Why Choose DD Wilson for Your Back Boiler Conversion?
DD Wilson Gas and Heating Engineers Ltd has been serving Liverpool, Wirral, and the wider Merseyside area since 1998, with over 27 years of trading history. Founded by Darren Wilson, the business has grown from a one-man operation into a team of experienced engineers covering a 35-mile radius from Liverpool city centre, including St Helens, Southport, Ormskirk, Runcorn, Chester, Birkenhead, and Ellesmere Port.
We are Gas Safe Registered (number 583586), Vaillant Advance Master Tech installers, and ATAG-approved engineers. Our customer reviews speak to the standard of work our team consistently delivers. You can also read about recent boiler upgrades across Liverpool, completed by our team, to get a sense of the work in practice.
Every back boiler conversion we carry out includes:
A full pre-installation survey at no charge
Gas Safe compliant removal of the back boiler, gas fire, hot water cylinder, and cold water tank
Professional installation of the new combi boiler with a full manufacturer's warranty
System power flush and magnetic filter installation
New flue installation to current Part L Building Regulations standards
Gas Safe Building Regulations notification submitted on your behalf
Full system commissioning, testing, and controls handover
Clean and tidy working practice throughout
We cover Liverpool, Wirral, Merseyside, Cheshire, South Lancashire, and Greater Manchester. Use our local areas page to confirm your postcode falls within our coverage zone.
Back Boiler Conversion: Frequently Asked Questions
Can I keep my gas fire if I remove the back boiler?
No. The back boiler and the gas fire in front of it are part of the same unit, sharing the same flue. When the back boiler is removed, the gas fire cannot remain in operation. The gas supply to the fireplace will be capped as part of the removal process. You may choose to install a separate decorative gas fire at a later date if there is an appropriate flue available, but this would be a separate project.
Will I need new radiators when I convert to a combi?
Not necessarily, but it depends on the condition and size of your existing radiators. If they are in good condition and correctly sized for each room, they can remain in place. If they are old, corroded, or undersized, our engineers will advise on upgrading them. We will assess this during the pre-installation survey so you know what to expect before any work begins.
How much can I save on my gas bills after a back boiler conversion?
This depends on your current boiler efficiency, the size of your property, and how you use your heating. In general terms, upgrading from a 65 per cent efficient back boiler to a 93 per cent efficient combi boiler can reduce your gas consumption for heating and hot water by 20 to 30 per cent. At current gas prices, that represents a meaningful annual saving for most Liverpool households.
Is a back boiler conversion covered by any government grants?
Eligibility varies based on your income, property EPC rating, and the specific scheme in operation at the time. The Boiler Upgrade Scheme has historically been focused on heat pump and biomass upgrades rather than gas boiler replacements. However, other energy efficiency grant programmes do exist and eligibility requirements change. Visit our government-backed scheme page for the most current information, or speak to our team who can advise based on your specific circumstances.
Do I need to notify anyone when a back boiler is removed?
Yes. Gas boiler installations, including conversions, are notifiable under Part J (gas) and Part L (energy efficiency) of the Building Regulations in England and Wales. DD Wilson handles all Gas Safe Building Regulations notifications on behalf of our customers for every installation. You will receive a Building Regulations Compliance Certificate at the end of the job, which is an important document for your property records and for any future sale.
How long does the new combi boiler warranty last?
Warranty terms vary by manufacturer and model. Vaillant offers up to 10 years warranty on the ecoTEC exclusive when installed by an Advanced Master Tech installer, such as DD Wilson, and registered within the required timeframe. Warranty terms are one of the reasons we recommend investing in a quality boiler rather than the cheapest available option; the long-term cost of ownership is lower when parts and labour are covered for a decade.
Can DD Wilson cover my area for a back boiler conversion?
DD Wilson covers Liverpool, Wirral, Merseyside, South Lancashire, Cheshire, and parts of Greater Manchester, serving a 35-mile radius from Liverpool city centre. Our areas we cover page lists all the towns and postcodes we serve regularly, including Bootle, Crosby, Maghull, Ormskirk, Southport, St Helens, Warrington, Runcorn, Birkenhead, Wallasey, Ellesmere Port, and Chester.
Related Reading
This article was originally published in 2024 and has been updated in March 2026 to reflect current boiler models, installation costs, and Building Regulations requirements.
Convert Your Back Boiler to a Combi Today
DD Wilson Gas And Heating Engineers Ltd has been installing, repairing, and upgrading heating systems across Liverpool and Merseyside since 1998. Family-run, Gas Safe Registered (583586), and Vaillant Advance Master Tech accredited, our team handles back boiler conversions from survey through to commissioning with no shortcuts and no surprises.
Call us: 0151 739 8945
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