Changing from a Conventional Boiler to a Combi Boiler

At Boilers 2 Go, we’ve helped many homeowners and landlords switch from a conventional boiler to a combi boiler, a transition that can transform space usage and efficiency in your property. 

If you’re pondering this upgrade—perhaps to ditch that bulky hot water cylinder and streamline your setup—this guide covers the essentials, from benefits to costs, drawing from real-world installs we’ve overseen to help you decide if it’s right for your home or rental.

Why Change from a Conventional Boiler to a Combi Boiler?

Changing from a conventional boiler to a combi boiler often makes sense if you’re looking to save space, boost efficiency, and enjoy instant hot water without storage tanks cluttering your airing cupboard. 

This transition suits compact UK properties where conventional systems with separate cylinders feel outdated, delivering on-demand heating that aligns with modern lifestyles while potentially trimming energy bills by 20-30% through better modulation.

Space Savings and Modern Convenience

Ditching the cylinder frees up valuable room for storage or conversions, a big win for landlords maximising rental appeal or homeowners in terraced houses.

What Are the Benefits of Switching to a Combi Boiler?

The benefits of switching to a combi boiler include enhanced energy efficiency, unlimited hot water on demand, and reduced installation complexity, making it a popular choice for UK upgrades. 

• Space Savings: Removes the need for a hot water cylinder and cold water storage tank, freeing up valuable loft or cupboard space for storage or other uses—ideal for smaller UK homes or landlords maximising rental appeal.
• Instant Hot Water on Demand: Heats water directly from the mains as needed, eliminating waiting times and providing unlimited supply without running out, perfect for busy households.
• Improved Energy Efficiency: Condensing technology achieves up to 92-94% efficiency (A-rated), reducing gas usage and bills by £100-£300 annually compared to older conventional systems.
• Lower Installation and Maintenance Costs Long-Term: Simpler setup with fewer components means easier servicing and fewer parts to fail, cutting ongoing expenses for homeowners.
• Reduced Risk of Leaks and Freezing: No tanks mean less chance of overflows or frozen attic pipes, a common headache in UK winters.
• Better Water Pressure: Draws directly from mains supply, often delivering stronger flow to showers and taps than gravity-fed conventional setups.
• Modern Controls Compatibility: Easily pairs with smart thermostats like Hive or Nest for remote management and zoning, enhancing comfort and savings.
• Eco-Friendly: Lower carbon emissions from higher efficiency, aligning with UK net-zero goals and potential eligibility for green home grants.

Check out our list of the best combi boilers on the market to help you find the perfect model for your property. 

What Are the Drawbacks of Changing to a Combi Boiler?

The drawbacks of changing to a combi boiler centre on potential hot water flow limitations in larger homes and the upfront disruption of removing old components. 

In our assessments, this sensitivity to mains pressure can mean slower simultaneous taps in multi-bathroom setups, why some prefer system boilers instead—plus, the conversion might involve rerouting pipes, causing temporary mess for occupied rentals. Read our guide on system vs combi boilers to learn more.

• Limited Hot Water for High Demand: Struggles with simultaneous use (e.g., multiple showers plus taps), leading to temperature drops in larger homes with 3+ bathrooms.
• Dependence on Mains Pressure: Performance relies on strong incoming water pressure—if low in your area, flow can be weak without additional pumps.
• Upfront Disruption and Cost: Conversion involves removing tanks and rerouting pipes, causing mess and expenses of £2,000-£4,000, plus potential downtime.
• Not Ideal for Very Large Properties: Higher kW models needed for big houses, increasing costs and potentially overwhelming standard mains supply.
• Cold Water Flow Impact: All cold taps run from mains too, so if pressure fluctuates, it affects the whole house—not just hot.
• Potential for More Frequent Faults in Hard Water Areas: Scale buildup can affect the heat exchanger faster without inhibitors or softeners.
• No Backup Storage: If the boiler fails, you lose both heating and hot water instantly, unlike conventional systems with stored reserves.
• Noise Levels: Some combis can be audible during operation, noticeable in open-plan living compared to quieter tank-fed setups..

How Much Does It Cost to Change from a Conventional Boiler to a Combi Boiler?

Changing from a conventional boiler to a combi boiler costs £2,000-£4,000 on average, including the unit (£800-£1,500), labour (£800-£1,500), and extras like pipework modifications (£200-£1,000). 

Based on our quotes for clients, expect lower ends for simple swaps in small flats, rising for larger homes needing cylinder removal and flue adjustments—factor in £100-£200 annual savings to recoup over 5-7 years.

Factors Influencing Cost

Location matters—urban areas add disposal fees for old tanks, while grants like ECO4 could subsidise for eligible low-income households.

Cost Savings Over Time

Lower running costs from no standby heat loss in cylinders can save £100-£200 yearly, plus easier compliance with UK efficiency regs for landlords.

What Is the Installation Process for Switching to a Combi Boiler?

The installation process for switching to a combi boiler involves removing the old conventional setup, fitting the new unit, and testing for leaks and efficiency, typically taking 1-3 days. From my installs, it starts with draining the system and dismantling cylinders, then mounting the combi with new pipe runs—always by Gas Safe engineers to ensure safe venting and compliance.

Preparation and Timeline

Prep by clearing space and scheduling during off-peak for minimal disruption; post-install, expect flushing to remove debris for optimal performance.

Is Changing to a Combi Boiler Suitable for My Home?

Changing to a combi boiler is suitable for your home if it’s small to medium-sized with good mains pressure and low simultaneous hot water needs, avoiding flow issues in bigger properties. In our evaluations, it’s perfect for 1-2 bathroom flats or semis but less ideal for large houses—test your mains flow (aim for 10-15 l/min) to confirm viability.

Assessing Mains Pressure and Property Size

Low pressure areas may require pumps; for landlords, combis simplify maintenance but check tenant demands first.

What Maintenance Is Required After Changing to a Combi Boiler?

Maintenance required after changing to a combi boiler includes annual Gas Safe servicing to check components, flush sediment, and ensure efficiency, costing £80-£150. From my service routines, this sensitivity to scale in hard water means adding inhibitors yearly, while weekly pressure checks (1-2 bar) catch drops early for longevity.

Long-Term Care Tips

Bleed radiators seasonally and monitor for unusual noises to keep the system running smoothly without breakdowns.

Ready to Switch? Get a Quote from Boilers 2 Go

Ready to switch from a conventional boiler to a combi? It’s a move that can modernise your heating, but professional advice ensures it’s right for you. Request a free, no-obligation quote on top combi models like Baxi or Ideal from Boilers 2 Go today. 

Whether you’re a homeowner after space savings or a landlord boosting property value, our experts will provide tailored options suited to your property.

FAQs

How does mains water pressure test for combi suitability?

Run a tap fully and time filling a 10-litre bucket—under 60 seconds indicates good flow for combis.

What pipework changes might be needed for the switch?

Removing cylinders often requires capping old pipes and adding new runs—pro surveys spot this early.

Are combis compatible with solar thermal systems?

Yes, pre-heated water from panels boosts efficiency—hybrid setups cut bills further.

How long does cylinder removal take during install?

1-2 hours typically, with pros handling disposal to avoid mess.

Can combis work with smart home hubs like Alexa?

Many integrate for voice control of heating schedules.