Conventional boilers, also known as regular or heat-only boilers, are the right choice for homes with a traditional open-vented heating system: a cold water storage tank in the loft and a separate hot water cylinder, usually in an airing cupboard. They are not suitable for properties looking to switch to a combi, but for houses where the existing pipework is already in place, they offer a straightforward, cost-effective upgrade with one important advantage over combis: a hot water cylinder that stores heated water ready for simultaneous use across multiple bathrooms.
If you are unsure whether a conventional boiler is right for your property, the guide on types of boilers for your home covers the differences clearly. For smaller properties that may be better served by a combi, the best boiler options for small homes guide covers the two-bedroom market. For larger properties with higher demand, the best boilers for four bedroom homes and best boilers for three bedroom homes articles cover the right sizing and brands for those property types.
This guide reviews the five best conventional boilers available in the UK for 2026, based on efficiency, warranty length, reliability data, installer feedback, and real-world customer satisfaction.
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5 Best Conventional Boilers: At a Glance
All five models are A-rated condensing boilers with a minimum efficiency of 92%. Trustpilot scores updated to June 2026. For a detailed comparison of what each warranty actually covers and the conditions attached, the top boiler warranties in the UK guide compares the major brands side by side.
| Boiler Model | Output (kW) | Efficiency | Max Guarantee | Which? | Trustpilot | Unit Price (est.) |
|---|---|---|---|---|---|---|
| Worcester Bosch Greenstar Ri | 9 to 30 | 92% | 12 years | Best Buy | 4.6/5 | £900 to £1,300 |
| Viessmann Vitodens 100-W Heat Only | 11 to 32 | 98% | 12 years | Recommended | 4.6/5 | £1,050 to £1,450 |
| Vaillant ecoTEC Plus Regular | 12 to 35 | 94% | 10 years | Best Buy | 4.5/5 | £1,000 to £1,500 |
| Ideal Logic² Max Heat | 12 to 30 | 93% | 10 years | Best Buy | 4.8/5 | £850 to £1,200 |
| Baxi 800 Heat | 16 to 30 | 93% | 10 years | Top Rated | 4.5/5 | £950 to £1,300 |
1. Worcester Bosch Greenstar Ri
The Worcester Bosch Greenstar Ri is the most widely recommended conventional boiler for UK homes where space is limited and installer support matters. Its compact dimensions are specifically designed to fit inside a standard kitchen cupboard, making it one of the few heat-only boilers that can genuinely be described as a cupboard-fit unit. Worcester Bosch has held the Which? Best Buy award for 16 consecutive years, and the Greenstar Ri benefits directly from that brand’s service network and parts availability.
The broader Greenstar range is worth understanding for context. The Worcester Bosch Greenstar 8000 features review covers the flagship combi version of the range for homeowners comparing heat-only versus combi options. The Worcester Bosch Greenstar 1000 features review covers the 1000 series for larger properties where higher outputs are needed.
Specs, Features, and Technology
The Greenstar Ri features a high-grade aluminium-silicon heat exchanger with excellent thermal conductivity. It is hydrogen-ready for a 20% blend and fully compatible with solar thermal installations, which reduces reliance on gas for domestic hot water during sunny months. Controls are deliberately straightforward: a simple dial interface that most homeowners can use without consulting a manual.
The Ri modulates its output to match the heating demand of the property, reducing gas consumption during milder weather. It is compatible with the Bosch EasyControl smart thermostat for app-based control if more advanced scheduling is needed.
Efficiency
ErP A-rated at 92% efficiency. The modulating burner ensures the boiler does not run at full output unnecessarily, which keeps annual running costs lower than the headline efficiency figure alone might suggest.
Estimated Costs
- Boiler unit only: £900 to £1,300
- With installation: £2,100 to £3,400
- Running costs: low, particularly when paired with Bosch EasyControl smart controls for demand-led operation
Which? and Trustpilot
Which? Best Buy for 16 consecutive years. Trustpilot 4.6/5. Engineers frequently praise the availability of spare parts and the ease of servicing the Greenstar range.
2. Viessmann Vitodens 100-W Heat Only
The Viessmann Vitodens 100-W in its heat-only configuration is the recommended choice for homeowners who prioritise engineering longevity and the lowest possible running costs over the boiler’s lifetime. At 98% efficiency it is the highest-rated heat-only boiler on this list, and its Inox-Radial stainless steel heat exchanger is rated for a potential service life of 15 to 20 years, compared to 10 to 12 for aluminium alternatives.
For a detailed cost breakdown and analysis of the 35kW version of this range, the viessmann 35kw boiler cost analysis covers the full picture including pipework and running cost projections. The Viessmann Vitodens 222F specifications review is also worth reading if you are comparing the heat-only 100-W against the 222-F system boiler with built-in hot water cylinder, which is an alternative for properties where cylinder space is limited.
Specs, Features, and Technology
The Vitodens 100-W uses the Inox-Radial stainless steel heat exchanger, which is more resistant to corrosion than aluminium and maintains performance better over time in hard water areas. The MatriX-Plus burner and Lambda Pro combustion control automatically adjust the gas-to-air mixture to maintain peak performance even when gas quality fluctuates, which is increasingly relevant as the UK gas network begins to incorporate hydrogen blends.
Built-in WiFi enables connection to the ViCare smart app for remote monitoring and control. Weather compensation is available as an optional accessory, which can deliver an additional 10% gas saving on top of the standard efficiency figure.
Efficiency
Seasonal efficiency up to 98%: the highest of any model reviewed here. At current 2026 gas rates, the annual saving over a 92% efficient boiler is approximately £44 per year in fuel costs alone. Over a 12-year warranty period that compounds to over £500 in gas savings before accounting for inflation.
Estimated Costs
- Boiler unit only: £1,050 to £1,450
- With installation: £2,200 to £3,600
- Running costs: the best long-term economics of the five models reviewed here, due to the combination of highest efficiency and longest exchanger life
Which? and Trustpilot
Which? Recommended Brand. Trustpilot 4.6/5 as of June 2026. Specialist heating engineers consistently rate the Vitodens 100-W highly for build quality and component durability. For a broader comparison of how Viessmann’s efficiency numbers stack up against Vaillant, the Viessmann boiler efficiency ratings guide provides a detailed side-by-side analysis.
3. Vaillant ecoTEC Plus Regular
The Vaillant ecoTEC Plus Regular is the recommended choice for properties where quiet operation is a priority: it holds the Quiet Mark accreditation, making it one of the few heat-only boilers independently verified for low noise output. This matters particularly in homes where the boiler is in or near a bedroom, bathroom, or open-plan living space.
Vaillant is a German manufacturer with a major production facility in Belper, Derbyshire, and one of the largest installer networks in the UK. The Potterton boiler cost analysis is worth reading alongside this section if you are comparing the ecoTEC Plus against a budget conventional alternative from a brand in the same ownership group.
Specs, Features, and Technology
IoniDetect technology monitors the quality of the gas flame in real time and adapts the air-to-gas ratio accordingly. This keeps combustion clean across the full range of operating conditions, reduces emissions, and maintains efficiency stability throughout the boiler’s life rather than just at the point of installation.
The ecoTEC Plus integrates with Vaillant’s vSMART app-based controls and supports Alexa and Google Assistant for voice-controlled heating. Available in outputs from 12 kW to 35 kW, covering small to large conventional heating systems. The series is also compatible with the Vaillant aroTHERM heat pump for future hybrid installation if decarbonisation becomes a priority.
Efficiency
94% seasonal efficiency with ErP A-rating. Vaillant’s HHIC warranty claims rate of 0.8 per 1,000 units (2025 data) is the lowest of any brand reviewed here, reflecting strong long-term reliability in practice.
Estimated Costs
- Boiler unit only: £1,000 to £1,500
- With installation: £2,300 to £3,700
- Running costs: competitive, particularly when combined with vSMART weather compensation controls
Which? and Trustpilot
Perennial Which? Best Buy award recipient. Trustpilot 4.5/5. Customers regularly highlight the quiet operation and professional warranty support. Vaillant’s installer network is one of the most extensive in the UK, reducing wait times for service appointments.
4. Ideal Logic² Max Heat
The Ideal Logic² Max Heat is the best value conventional boiler for homeowners who want a comprehensive package rather than just the unit. It ships with a high-quality magnetic system filter in the box, has an industry-leading 4.8 out of 5 Trustpilot rating from over 66,000 reviews, and is manufactured in Hull, making it the only British-built boiler on this list.
The Logic² Max Heat is the heat-only equivalent of the combi reviewed in the ideal logic c30 boiler cost analysis, which gives useful context on the overall Logic range quality and where the Max specification sits within it. For a broader comparison of Ideal’s positioning against Baxi, the ideal boiler features and efficiency guide covers both brands in detail.
Specs, Features, and Technology
The Ideal System Filter included in the box is a meaningful inclusion: sludge and magnetite build-up is the leading cause of boiler failure on older UK heating systems, and including the filter at no extra cost means the heat exchanger is protected from day one without an additional purchase. A large, high-definition colour display shows full plain-text fault descriptions rather than fault codes, reducing unnecessary engineer call-outs for minor issues.
Compatible with the Hive and Halo smart thermostat ranges for app-based scheduling and remote control. Compact dimensions for a heat-only boiler: fits inside a standard kitchen cupboard despite supporting outputs up to 30 kW.
Efficiency
93% A-rated efficiency. Modulates down to very low outputs to prevent short-cycling, which reduces burner wear and maintains efficiency during periods of lower demand.
Estimated Costs
- Boiler unit only: £850 to £1,200
- With installation: £2,000 to £3,100
- Running costs: the included filter reduces powerflush frequency over the boiler’s life, lowering total maintenance cost versus boilers where this is an optional extra
Which? and Trustpilot
Which? Best Buy. Trustpilot 4.8/5 from over 66,000 reviews: the highest of any brand in this review. Customers and engineers consistently cite the clarity of the fault display and the responsiveness of Ideal’s warranty team as standout features.
5. Baxi 800 Heat
The Baxi 800 Heat is the recommended conventional boiler for direct replacement scenarios, particularly where the property already has a Baxi or Potterton boiler installed. The 800 Heat uses a central flue design that frequently makes it a direct like-for-like swap for discontinued legacy models, which reduces installation time and labour cost by avoiding the need to move existing pipework.
For a broader comparison of how Baxi performs against Alpha in the value conventional boiler segment, the alpha boilers product comparison insights guide covers that side-by-side. The Viessmann boiler efficiency ratings comparison is also useful if you are deciding between the Baxi and a premium German alternative.
Specs, Features, and Technology
The Baxi 800 Heat ships with an ADEY Micro2 magnetic system filter included in the package, which protects the heat exchanger from magnetite and sludge from the point of installation. At approximately 19.5 kg in its lightest configuration, it is one of the lightest conventional boilers available, which makes installation easier in tight loft spaces or awkward airing cupboard locations.
The central flue design is a practical advantage in replacement scenarios: it aligns with the flue positions used by many older Baxi, Potterton, and Main boilers, making it a straightforward swap that minimises disruption. Compatible with a range of smart thermostats through standard two-wire connections.
Efficiency
ErP A-rated at 93% efficiency. Designed for rapid response: heating reaches radiators almost immediately when the programmer signals demand, which is particularly useful in larger properties with longer pipe runs between the boiler and the furthest radiators.
Estimated Costs
- Boiler unit only: £950 to £1,300
- With installation: £2,100 to £3,300
- Running costs: predictable and in line with the industry average for a 93% A-rated conventional boiler
Which? and Trustpilot
Which? Top Rated. Trustpilot 4.5/5. Landlords and property managers cite Baxi’s parts availability through local plumbing merchants as a key advantage for reducing repair downtime across multiple properties.
How to Choose the Best Conventional Boiler
Selecting the right conventional boiler involves three key variables: the property’s heat demand, the existing system’s compatibility, and how long you intend to stay in the property.
For guidance on matching output to your home’s actual heat demand, the boiler size recommendations for households guide covers the calculation in detail. Understanding the average boiler lifespan for homes helps frame the warranty comparison: a 10-year warranty is meaningless if the boiler only lasts 8 years, and a 12-year warranty is good value if the boiler reaches 15.
| Boiler | Choose if… | Avoid if… |
|---|---|---|
| Worcester Bosch Greenstar Ri | You want a compact fit-and-forget cupboard boiler backed by the UK’s most trusted brand and the widest engineer network | You live in a hard water area and want a stainless steel heat exchanger for maximum mineral resistance |
| Viessmann Vitodens 100-W Heat Only | You want the highest efficiency (98%), a stainless steel heat exchanger rated for 15 to 20 years, and the longest-life heat-only boiler available | You prefer a brand where every local independent engineer is likely to carry spare parts in their van |
| Vaillant ecoTEC Plus Regular | The boiler is located near a bedroom or living area and you need the quietest operation possible, confirmed by Quiet Mark accreditation | You are on a strict budget; Vaillant sits at the more premium end of the pricing scale |
| Ideal Logic² Max Heat | You want the best all-in-one value: magnetic filter included in the box, 10-year warranty as standard, and the highest Trustpilot score of any brand reviewed here | You need the absolute highest efficiency; Viessmann at 98% outperforms Ideal at 93% |
| Baxi 800 Heat | You are replacing an older Baxi or Potterton boiler and want a lightweight, direct-replacement unit that minimises installation time and labour cost | You want the most advanced smart control integration or the longest guarantee available |
Ready to Get a New Boiler Quote?
Upgrading to a modern A-rated conventional boiler is one of the most cost-effective heating improvements available for homes with a traditional open-vented system. If your current boiler is over 10 years old, it is likely operating below 80% efficiency, meaning more than 20p in every pound spent on gas is being wasted.
If the installation involves repositioning the boiler to a better location within the property, the understanding boiler relocation expenses guide covers what repositioning typically adds to the total cost before you request quotes.
Boilers 2 Go provides fixed-price installations across the UK, often available the next day. Request a free, no-obligation quote and our team will recommend the right model and output for your specific system.
FAQs
Can I use a conventional boiler with underfloor heating?
Yes. Conventional boilers are well suited to underfloor heating (UFH) systems. Because they work with a hot water cylinder that stores a large volume of heated water, they can deliver the consistent, low-temperature flow that UFH manifolds require. A mixing valve must be installed to reduce the flow temperature from the boiler to the 35 to 45 degrees Celsius typically used for underfloor circuits. A Gas Safe engineer will specify and fit the correct mixing valve as part of the installation.
Is it possible to convert a conventional system to a combi later?
Yes, but it is a significant job. Converting from a conventional to a combi involves removing the cold water storage tanks in the loft and the hot water cylinder, re-routing pipework to accept mains-pressure water, and upgrading the gas supply pipe if the new boiler requires a higher flow rate. If a future combi conversion is on your plans, the most cost-effective approach is to carry out the conversion at the same time as fitting the new boiler, rather than as a separate job later. For more detail on switching boiler types, the guide on types of boilers for your home covers the differences between system types and the practical implications of converting.
Do modern conventional boilers still require a header tank?
Modern regular (heat-only) boilers are most commonly installed as part of an open-vented system, which does require a small feed-and-expansion tank (header tank) in the loft. However, some models can be configured as part of a sealed system using an external expansion vessel and filling loop, which removes the need for loft tanks while retaining the existing hot water cylinder. A Gas Safe engineer can advise on whether your system can be sealed based on your existing pipework and cylinder type.
How do I know if my conventional boiler is hydrogen-ready?
All five models reviewed here are certified as 20% hydrogen-ready, meaning they are tested to run on a blend of natural gas and 20% hydrogen without modification. This is the current direction of UK government gas network policy. Look for an H2 Ready logo or sticker on the front casing, or check the manufacturer’s technical data sheet. Any boiler manufactured from 2024 onwards from a mainstream UK brand should carry this certification as standard.
Why does a conventional boiler need a separate pump?
Unlike combi or system boilers, which have the circulation pump built into the boiler casing, a conventional heat-only boiler relies on an external pump, typically located in the airing cupboard near the hot water cylinder. This pump circulates heated water around the radiator circuit and through the coil in the hot water cylinder. Because the pump is external and accessible, replacement is usually straightforward and does not require a boiler specialist for the pump work itself, which keeps maintenance costs lower than on some sealed system configurations.
How often should a conventional boiler be serviced?
Annual servicing by a Gas Safe registered engineer is the standard recommendation and the condition required to keep most manufacturer warranties valid. A full service on a conventional boiler includes checking the heat exchanger, burner, flue integrity, pump operation, cylinder thermostat, zone valves, and system pressure. The cost typically runs between £80 and £120. For landlords, annual gas safety checks are a legal requirement under the Gas Safety (Installation and Use) Regulations 1998 and must be documented and provided to tenants.
Article published by Penny North, Home Energy Heating Expert at Boilers2Go.
I’m Penny North, a home energy heating expert. My mission is to demystify new boilers and complex heating systems to help you achieve a warm, cosy home with lower energy bills and a smaller environmental footprint.