Looking for the best 30kW combi boiler for your home?

In this guide, we take a straight-talking look at the most popular 30kW combi boilers out there. We focus on what actually matters in the real world—hot water flow rate, modulation ratio, and overall efficiency—so you can pick the right one for your home, budget, and lifestyle. Whether you’re swapping out an old unit or fitting a new boiler or a new system, we give you clear, unbiased advice to help you choose with confidence.

What to Look For in a 30kW Combi Boiler

Before comparing models, it’s worth understanding the two key factors that make the biggest difference:

1. Modulation Ratio

This tells you how much a boiler can turn its output up or down depending on demand. A higher modulation ratio means better efficiency and lower gas bills, especially in homes that don’t always need full power. It also means quieter, more consistent heating.

2. Hot Water Flow Rate

Measured in litres per minute, this shows how much hot water a boiler can deliver at once (at Δ35˚C) . If you’ve got a large household or use multiple taps and showers, a higher flow rate helps you avoid pressure drops and keeps things running smoothly.

Now that we’ve covered the basics, let’s look at how the top models stack up in 2025.

Top 30kW Combi Boilers for Hot Water Flow Rate and Efficiency

Boiler Model	Modulation Ratio	Minimum Output	Hot Water Flow Rate (at 35°C rise)
Worcester Bosch Greenstar 4000	1:10	3 kW	12.3 l/min
Worcester Bosch Greenstar 2000	1:6	4.8 kW	10.8 l/min
Vaillant ecoFIT Pure 30kW	1:5	6.3 kW	12.2 l/min
Vaillant ecoTEC Plus 32kW	1:10	3.5 kW	13.0 l/min
Baxi 800	1:5	6 kW	12.2 l/min
Main Eco	1:5	6.2 kW	12.2 l/min
Viessmann Vitodens 025-W 28KW	1:5	5kW	12.0 l/min
Viessmann Vitodens 200-W	1:17	1.9 kW	12.4 l/min
Ideal Logic 2	1:4	6.1 kW	12.4 l/min
Ideal Vogue Gen 2 32Kw	1:5	4.6 kW	13.1 l/min
Navien NCB 500	1:6	4.5 kW	13.3 l/min

Best Combi Boilers for Hot Water Flow Rate

If hot water flow rate is crucial to your decision-making, then boilers like the Vaillant ecoFIT Pure 30kW, Baxi 800, and Navien NCB 500 stand out. They all offer around 13.0 litres per minute, providing consistent and strong hot water flow — ideal for larger homes or properties with multiple bathrooms.

Thinking about upgrading? Our expert team can help with professional boiler installation to ensure your new combi boiler performs at its best.

• • Vaillant ecoFIT Pure 32kW: German-engineered and compact, this boiler delivers a solid 12.2 l/min flow rate, making it a dependable choice for families with high hot water demand.

  • Baxi 800 30kW: Also rated at 12.2 l/min, this UK-made boiler includes a 10-year warranty with Adey filter, offering both performance and value.

  • Navien NCB 500: With a 13.3 l/min flow rate and 1:6 modulation, it balances high hot water output with good efficiency. Though newer to the UK, Navien is a global leader in heating technology.

  • Ideal Logic 2 30kW: Also offers 12.4 l/min flow and a 1:4 modulation ratio. It’s a strong all-rounder with a reputation for reliability and good manufacturer support.

  • Worcester Bosch Greenstar 4000 30kW: Delivers 12.3 l/min flow, with excellent reliability, quiet operation, and a wide 1:10 modulation ratio. Ideal for homes with one to two bathrooms that want trusted performance and top energy efficiency.

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Why Modulation Ratio Matters for Smaller or Well-Insulated Homes

If your home is well-insulated or not constantly demanding full heat, a boiler with a wide modulation ratio (like 1:10 or more) can improve comfort and reduce energy waste. Instead of switching on and off frequently, the boiler runs smoothly at lower output — saving gas, reducing noise, and minimising wear and tear.

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Best Combi Boilers for Modulation Ratio

For those focused on efficiency and fuel savings, the following boilers stand out for their high modulation performance:

• Viessmann Vitodens 200-W: With an industry-leading 1:17 modulation ratio, this boiler can run very low and very efficiently. Ideal for homes with varying heating needs. It’s a premium model with a premium price tag.

• Worcester Bosch Greenstar 4000: Offers 1:10 modulation, excellent build quality, and strong support across the UK. It also maintains a respectable hot water flow rate of 12.3 l/min.

• Vaillant ecoTEC Plus 32kW: Modulates at 1:10 and supports a wide range of third-party controls. It’s more advanced than the ecoFIT model and offers very quiet, efficient operation.

• Navien NCB 500: With a 1:6 modulation ratio, it sits slightly lower but still offers a strong balance between flow rate and smart control features.

Ready to install your chosen boiler? Our professional boiler installation service ensures it’s set up perfectly for your home.

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Best Budget Combi Boilers 

Whether you’re a landlord or someone looking for a budget boiler that’s still reliable and efficient, these models are solid choices:

• Main Eco Compact 30kW: With a 1:5 modulation ratio and made by Baxi, this boiler gives good efficiency, solid performance, and a 5-year warranty. A smart choice for tight budgets.

• Ideal Logic 2 30kW: Offers a good balance of flow (12.4 l/min), reliable brand support, and decent modulation (1:4). A good all-rounder for everyday needs at a competitive price.

No matter your situation, we ensure every boiler installation is done right—no cutting corners, no dodgy pipework—just reliable, high-quality work you can trust, even on a budget.

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Warranty and Reliability

Most boilers listed here offer a 10-year warranty if installed by an approved installer. Ideal Logic Vogue goes a step further with a 12-year warranty, making it appealing for homeowners looking for long-term peace of mind.

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Which Boiler Is Right for Your Home?

Quick Summary of Our Top Combi Boiler Picks:

• Worcester Bosch Greenstar 4000: Ideal for homes requiring efficient modulation and reliable performance.

• Vaillant ecoTEC Plus 32kW: Premium build and advanced controls with 1:10 modulation.

• Viessmann Vitodens 200-W: Top-tier modulation and tech, best for those willing to pay for best tech.

• Navien NCB 500: High flow rate with good modulation, suitable for busy households.

• Main Eco and Ideal Logic 2: Great options for people on a budget looking for reliable and efficient boilers.

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Final Thoughts: Choosing the Best Boiler for You

A great combi boiler should give you the hot water you need, run efficiently, and suit your budget. Brands like Worcester Bosch, Vaillant, Viessmann, and Navien offer excellent solutions — while models like Main Eco and Ideal Logic 2 are perfect for anyone needing performance at a lower cost.

At A Tech Installs Ltd, we supply and install all the models above. Not sure which boiler fits your home? Get in touch for honest advice and expert fitting.

We offer professional boiler installation across the Leeds area and would be happy to assist with advice and installation to suit your needs

Helpful Resources:

• Boiler Service Cost in Leeds – Full 2025 Guide
  Everything you need to know about what’s included, how long it takes, and average pricing.

• Gas Safety Certificate for Landlords – Cost & Legal Requirements Explained
  If you’re a landlord, this guide covers annual checks, CP12 certificates, and common issues.

• Boiler Installation Leeds – 2025 Guide for Homeowners
  Our complete guide to new boiler installations in Leeds—costs, what’s included, timeframes, and key tips.

Note: We aim to provide the most accurate and up-to-date information possible, but boiler models can get upgraded and specifications (like flow rate, modulation ratio, or even warranty lengths) may change over time. Manufacturers also occasionally offer extended warranties as part of special promotions.

If you’d like the latest details or want to know more about other manufacturers or different boiler models not listed here, feel free to contact us directly — we’re always happy to help .And if a new boiler isn’t the right move for you, we also offer boiler repairs to keep your current system going, or air source heat pump installations if you’re considering a more energy-efficient heating solution.

Last updated 02 July 2025

Best regards,
Attila from A Tech Installs