Knowing the worst boilers to avoid in 2025 can save you from frequent repair costs, frustrations, and unreliable performance in winter.

The use of gas boilers is expected to decrease in the future as we transition to low-carbon alternatives. However, for the moment, boilers still dominate the UK heating market. A report by the European Heating Industry shows that condensing boilers remain the most popular home heating technology in the UK, with 2023 and 2024 sales totalling over 1.5 million and over 1.3 million units, respectively.

Understanding which boiler brands consistently underperform is just as important as knowing the best when you’re in the market for a new boiler. You’ll live with the boiler you choose for 10 to 15 years, and it will determine whether you have hot water and your home stays warm and comfortable.

The last thing you want is to spend your hard-earned money on one of the worst boilers and end up with over a decade’s worth of headaches, repeated breakdowns, and endless calls to engineers. Knowing which boilers experts recommend avoiding can ensure you select alternatives that deliver genuine peace of mind.

Key Takeaways on the Worst Boilers to Avoid:

• Reliability matters more than price. The cheapest boilers often become the most expensive to maintain over 10 to 15 years.
• Ferroli, Vokèra, Keston, and Biasi are the brands most frequently reported for faults, poor parts availability, and short warranties.
• All modern boilers meet Boiler Plus efficiency standards (92%+), so the real differences come down to build quality, customer service, and warranty strength.
• Top-rated alternatives include the Worcester Bosch Greenstar 4000, Ideal Logic Max, Viessmann Vitodens 100-W, and Vaillant ecoTEC Plus.
• A long guarantee is a key indicator of quality. Aim for a 10–12-year guarantee from an accredited installer.
• Regular servicing keeps a boiler efficient and covered. Schedule annual maintenance to prevent faults and protect warranty validity.
• Reliable after-sales support and easy parts access are what separate the best boilers from those most likely to cause breakdown stress.

How We Rated the Worst Boilers in 2025

To make sure the results are fair, this comparison is based on real data rather than opinions or marketing claims. Every boiler mentioned was evaluated using reliable public information, consumer feedback, and independent survey results. The following factors were used to determine which boilers performed poorly across the board:

• Which? reliability scores — Analysis of annual UK general public surveys covering thousands of homeowners responsible for maintaining their boilers and Gas Safe engineers who installed, repaired or serviced boilers in the past six years.
• Trustpilot ratings and verified customer reviews — Highlighting recurring service and fault complaints.
• Warranty and guarantee terms — Whether a brand offers a standard warranty or a full guarantee, and for how long.
• Parts availability — How easy it is to source replacement components when faults occur.
• Common breakdown types — Including ignition issues, leaking heat exchangers, and control board failures.
• After-sales service quality — Based on customer feedback about callout response times and communication.
• Engineer feedback — What installers say about build quality, ease of servicing, and long-term reliability.
• Efficiency and compliance — Ensuring all models have high energy efficiency ratings and meet Boiler Plus standards (minimum 92% efficiency).

Which are the Worst Boiler Brands and Models?

Independent surveys, installer feedback, and verified customer reviews reveal a small but consistent group of boiler brands that struggle with reliability, spare-part availability, or after-sales support.

Ferroli

Ferroli continues to appear at the bottom of engineer-recommendation lists for reliability. Results from the latest survey by Which? rank Ferroli at the bottom of the table with vetted heating engineers not rating them at all. They also note that the build quality of Ferroli boilers is poor and that it’s often challenging to find parts and do repairs.

The brand’s customer score is also low, and installers are generally not fans of the quality of help offered by the manufacturer.

Customer reviews often mention long waiting times for parts, limited service availability, and inconsistent after-sales communication. While newer Ferroli models, such as the Bluehelix series, have improved efficiency, the brand still carries a legacy reputation for poor durability.

Typical Issues

• Poor build quality
• Low customer score, limited service availability, and inconsistent after-sales communication
• Difficult to repair and access replacement parts

Warranty: 2 years standard, with optional extensions up to 5 years when installed by accredited engineers.

Better alternatives: Worcester Bosch Greenstar 4000 or Viessmann Vitodens 050-W, both known for superior after-sales care and stronger ten-year guarantee options.

Vokèra (by Riello)

Vokèra models, particularly the Vision 30C, have been criticised for frequent ignition and pressure faults, as well as reliability concerns once the initial warranty expires. The customer service is described as abysmal, with one installer on Trustpilot saying he lost long-term customers because of the unreliability of Vokèra boilers.

Engineers often describe them as serviceable but “not built for the long run,” mainly due to lightweight internal components and lower-cost control boards.

Although Vokèra boilers meet Boiler Plus standards and offer reasonable efficiency, the shorter warranty periods and variable customer-service experience place them below class leaders. Replacement parts are available, but can take longer to source outside major cities, leading to extended downtime when repairs are needed.

Typical Issues

• Ignition lockouts and pressure loss
• PCB and fan failures
• Poor customer service
• Uneven heating during prolonged use

Warranty: 5 years standard on most models, up to 7 years with approved installers.

Better alternatives: Ideal Logic Max Combi (10-year guarantee) or Vaillant ecoTEC Pro for households prioritising durability and responsive service networks.

Keston

Keston boilers have gained attention in the UK market for their space-saving flue system design, which allows long flue runs and flexible installation. However, when it comes to long-term reliability and user satisfaction, they have struggled to keep pace with competitors in 2025. Feedback from both homeowners and engineers frequently highlights difficulties sourcing replacement parts, limited service coverage, and faults developing sooner than expected.

Although Keston has few reviews on Trustpilot, a whopping 65% of previous customers give the brand a 1-star rating. Many criticise its unreliable services, with customers spending thousands of pounds on parts and repairs despite the boiler being under warranty.

They also note that many engineers will not come out to fix Keston boilers because they don’t trust that they won’t develop faults later. Independent installers note higher-than-average callout rates within the first five years, particularly linked to sensor errors and control board faults.

Typical Issues

• Frequent F1 and F2 error codes
• Unreliable customer service
• Delayed part delivery and specialist repair requirements

Warranty: 5 years standard; 7 years when installed by a Keston-accredited engineer.

Better alternatives: Ideal Logic Max or Vaillant ecoFIT Pure. Both share a similar compact profile but outperform Keston on reliability and service access.

Biasi

Biasi has long positioned itself as a budget-friendly boiler manufacturer, but its models regularly appear in engineer surveys as examples of “you get what you pay for.” While the upfront cost is appealing, customers often report frequent breakdowns, low build quality, and a noticeable drop in efficiency within a few years.

Which? survey results show Biasi boilers aren’t well-liked by owners and engineers, with most not having anything positive to say about the brand. Installers and owners frequently mention noisy operation and unreliable ignition that results in expensive repair costs just outside warranty.

Typical Issues

• Faulty fans and ignition modules
• Quick drops in efficiency after a few years
• Short operational lifespan without frequent maintenance

Warranty: 2 to 5 years, depending on the model, typically shorter than leading competitors.

Better alternatives: Alpha E-Tec Plus or Worcester Bosch Compact, both offering longer warranties and sturdier components without a significant price increase.

Best Alternatives to the Worst Boilers in 2025

If you’re upgrading your heating system, choosing a boiler from a trusted brand can mean years of dependable service, quieter operation, and lower repair costs. The following models stand out in 2025 for their strong reliability records, excellent support, and long guarantees. Each option below is a proven alternative to the underperforming brands listed earlier.

Worcester Bosch Greenstar 4000

Widely regarded as one of the most dependable combi and system boilers available, the Greenstar 4000 offers a blend of premium build quality and efficiency. Owners consistently rate it highly for quiet performance, responsive customer service, and minimal need for repairs. Its stainless-steel heat exchanger ensures longevity, while Worcester’s guarantee covers up to 12 years when installed by an accredited engineer.

Key advantages

• 94% efficiency and A-rated energy performance
• Compact casing suitable for cupboards
• Exceptional aftercare and UK-based support

Typical price: £950–£1,250 (boiler only)

Ideal Logic Max Combi

Manufactured by Ideal Heating, this model remains one of the best-balanced boilers in terms of price, warranty, and reliability. It features brass components for durability, built-in frost protection, and a 10-year guarantee when installed by a Max-accredited fitter. The Logic Max performs particularly well in smaller to medium-sized homes.

Key advantages

• 10-year full parts and labour guarantee
• Proven reliability and easy servicing
• Affordable without compromising build quality

Typical price: £850–£1,050 (boiler only)

Viessmann Vitodens 100-W

The Vitodens 100-W has long been known for its engineering precision. Manufactured in Germany and adapted for UK installations, it combines excellent heat efficiency with an intuitive digital control system. Its stainless-steel Inox-Radial heat exchanger provides outstanding corrosion resistance and thermal efficiency.

Key advantages

• 94% efficiency with modulating burner technology
• Long 10-year warranty
• Compact, modern design with Wi-Fi connectivity

Typical price: £900–£1,200 (boiler only)

Vaillant ecoTEC Plus

Vaillant’s ecoTEC Plus range remains a benchmark for quiet operation and energy savings. Many engineers recommend it for its solid internal components and ease of servicing. It’s especially well-suited to homes that need reliable hot-water flow rates for multiple outlets.

Key advantages

• Low operating noise and consistent heating
• Up to a 10-year warranty with Vaillant Advance installers
• Strong parts availability and support network

Typical price: £900–£1,150 (boiler only)

Alpha E-Tec Plus

A high-value option for homeowners who want premium reliability at a moderate price. It features a stainless-steel heat exchanger, a reliable Grundfos pump, and a 10-year warranty. Despite being classed as a budget model, it performs well in long-term reliability tests.

Key advantages

• Competitive price-to-performance ratio
• 10-year warranty
• Solid support record for a mid-range brand

Typical price: £750–£950 (boiler only)

Wondering how much a new boiler costs? Check out our guide on options available if you need a new boiler but can’t afford it, as well as boilers on finance and government boiler grants here.

Choosing one of these models can save you hundreds of pounds in potential repair costs and ensure consistent heating year-round. Look for a minimum 10-year guarantee and installation by an accredited engineer to keep warranty coverage valid.

How Does the Warranty of the Worst Boilers Compare to Alternatives?

Reliable warranty coverage is one of the clearest signs of a manufacturer’s confidence in its product. Brands that limit standard cover to only two or three years often do so because their failure rates are higher, or because parts are more expensive to replace once faults arise.

In contrast, leading manufacturers offer ten- to twelve-year guarantees as standard when fitted by accredited installers.

Below is a comparison of how the lower-rated boiler brands perform against trusted alternatives in 2025:

Brand	Standard Warranty (Years)	Extended Option	Guarantee or Warranty	Support Notes
Ferroli	2	Up to 5	Warranty	Limited UK coverage; parts often delayed
Vokèra	5	Up to 7	Warranty	Moderate support; response times vary
Keston	5	Up to 7	Warranty	Specialist servicing required; long flue design can complicate repairs
Biasi	2–5	Up to 7	Warranty	Basic coverage; must be serviced annually to remain valid
Worcester Bosch	7	Up to 12	Guarantee	Full UK network and quick part replacements
Ideal Heating	7	Up to 10	Guarantee	Extensive engineer availability
Vaillant	7	Up to 10	Warranty	Reliable support and fast parts delivery

A “guarantee” is stronger than a “warranty.” A guarantee ensures full cover during the term regardless of fault type, while a warranty often includes conditions and exclusions.

Who offers the best boiler deals in the UK? Check out our review of online boiler installation companies, boiler brands and the best UK boilers.

Final Thoughts on the Worst Boilers to Avoid

Selecting a boiler is one of the most important long-term home decisions you’ll make. A poor choice can lead to persistent faults, rising repair costs, and years of inconvenience. The brands listed earlier are not inherently unsafe, but repeated consumer feedback and engineer reports show that some models have struggled to meet modern standards for reliability, customer service, and durability.

Reliability and warranty coverage should outweigh small differences in price or advertised efficiency. Modern boilers must all meet the same energy-efficiency threshold, so the real value lies in build quality, parts support, and aftercare. Spending slightly more on a model with a decade-long guarantee often proves cheaper in the long run than saving a few hundred pounds upfront on a boiler prone to early faults.

Before making your final decision, confirm installation through a Gas Safe–registered engineer, check the warranty registration process, and ensure annual servicing is maintained. A well-chosen boiler should provide efficient, dependable heating for more than a decade instead of a recurring list of repair appointments.

FAQs on the Worst Boilers to Avoid

Which Boiler Brands Have the Most Problems?

Brands that most frequently appear in engineer reports and consumer feedback for reliability issues include Ferroli, Vokèra, Biasi, and Keston. Common complaints involve frequent breakdowns, limited spare-part availability, and shorter warranty coverage. These models often cost less upfront but tend to incur higher maintenance costs over time.

Which Boiler Brand Is the Most Reliable?

Worcester Bosch, Viessmann, and Ideal Heating are rated among the most reliable boiler brands in the UK. These manufacturers provide long warranties, robust build quality, and nationwide service networks, making them reliable long-term investments.

What Boilers Do Plumbers Recommend for a Combi Boiler?

Gas Safe engineers frequently recommend combi boilers like Ideal Logic Max, Worcester Bosch Greenstar 4000, and Vaillant ecoTEC Plus. These models are easy to service, energy efficient, and come with long guarantees. They also maintain high flow rates for households needing consistent hot-water pressure.

What Is the Most Common Problem with the Worst Boilers?

The most common boiler issues include pressure loss, ignition failure, and sensor or PCB faults. These problems often arise from ageing components, low water pressure, or neglected servicing. Scheduling an annual service and keeping the boiler’s pressure between 1.0 and 1.5 bar can prevent most of these faults.

Which Boiler Lasts the Longest?

Modern condensing boilers from top manufacturers can last 15 years or more with proper maintenance. The key factor in longevity is not just the brand but annual servicing, the quality of installation, and adherence to warranty terms.

Sources and References

The European Heating Industry – Heating Market Report 2024

Which? – Best gas and oil boiler brands

Trustpilot – These boilers are absolutely shocking

Trustpilot – Kreston Boilers