Best Combi Boiler 2026

Heating and hot water matter in every UK home.

If you are searching for the best combi boiler in 2026, you are usually trying to do two things.

First, you want a boiler that suits your household and delivers steady hot water without constant hassle.

Second, you want to avoid surprise costs by choosing a model with sensible warranty coverage and long term support.

This page is written for typical UK homes on mains gas that are replacing an older combi boiler.

If your property has unusual requirements, such as very low mains pressure or multiple bathrooms used at the same time, the final recommendation may change after basic checks.

All figures in this guide are taken from the model spec lists shown below and checked at the time of the last update.

What is a combi boiler

A combination boiler, usually shortened to combi boiler, provides central heating and hot water from one unit.

Hot water is produced on demand, so you do not normally need a hot water cylinder.

Combi boilers are popular because they save space and are simple to run.

They work best when the boiler output and hot water flow rate match your household demand and your mains water pressure is suitable.

If you want one practical takeaway here, it is this. Combi performance is not only about the boiler you choose.

It is also about how well it fits the property, how it is installed, and how it is maintained over time.

How we picked the best combi boilers for 2026

We compared each model using the same homeowner focused checks, based on the figures shown in each boiler’s spec list.

• Warranty coverage and length

• Hot water flow rate in litres per minute

• Power output in kW

• Energy efficiency rating

• Boiler dimensions and practical fit

• Controls and smart compatibility

Most warranties require annual servicing to remain valid.

This is worth factoring in at the start, because it affects warranty coverage and long term ownership cost.

What hot water flow rate means

The flow rate is a useful guide to hot water performance for showers and taps.

It is measured in litres per minute, and higher figures generally indicate stronger delivery.

In real homes, the actual result depends on:

• mains water pressure

• how cold the incoming water is, especially in winter

• how much the boiler needs to raise the temperature

• whether you are running hot water in more than one place at a time

If your household often uses hot water at the same time, flow rate becomes more important.

If you mostly use one shower or one tap at a time, you can be more flexible.

A note on independent signals

You may see independent badges, accreditations, and customer review signals used when comparing boilers.

These can be helpful context, but they should support the core checks above.

For most homeowners, correct sizing, warranty coverage, servicing requirements, and installation quality matter more than any single badge.

What can change the final recommendation

Even if you pick the right boiler on paper, a few real world checks can change the final model choice.

Common examples include:

• limited space for pipework, clearances, or servicing access

• the flue route and whether extra bends are needed

• mains pressure concerns

• heat loss and radiator demand

• whether controls upgrades are required

• any system clean or remedial work needed at installation stage

This is normal. A good recommendation should be based on your home, not just a headline list.

What is the best combi boiler uk 2026

Best combi boiler overall: Worcester Bosch Greenstar 4000
Best combi boiler for a smaller property: Alpha E-Tec NX
Best combi boiler for a larger property: Viessmann Vitodens 100-W

Top 5 combi boilers

Below are our five picks for 2026, with pricing guides, warranty coverage, size, hot water flow rate, and controls.

Installed cost depends on factors like access, flue position, controls, and whether any system upgrades are needed, so treat all installed prices as guides.

1. Worcester Bosch Greenstar 4000

• Price, inc install (guide): £2,865

• Warranty: 10 years

• Energy efficiency: A rated (94%)

• Power output: 30 kW

• Water flow rate: 12.3 L per minute

• Size: 724 mm (h) x 400 mm (w) x 310 mm (d)

The Worcester Bosch Greenstar 4000 is a strong all round option for many UK homes. It balances heating output and hot water delivery in a way that suits lots of typical households.

It also includes features designed to reduce wasted water at the tap, which can improve day to day convenience.

Expert opinion: We rank it highly because the hot water flow rate and output suit a wide range of homes, the controls are simple to use, and the warranty coverage is strong for a mainstream combi.

2. Alpha E-Tec NX

• Price, inc install (guide): £2,455

• Warranty: 11 years

• Energy efficiency: A rated (94%)

• Power output: 28 kW

• Water flow rate: 12.1 L per minute

• Size: 712 mm (h) x 440 mm (w) x 255 mm (d)

The Alpha E-Tec NX is a sensible choice for smaller properties where space matters.

Its depth helps when cupboard fit is a priority, but you still need to confirm clearances and servicing access.

It supports OpenTherm and Alpha BUS control options, which can improve comfort by helping the boiler modulate more smoothly with the right thermostat.

Expert opinion: We rate it because the compact 255 mm depth makes it easier to fit in many homes, while the 11 year warranty coverage helps reduce risk and long term surprise costs.

3. Worcester Bosch Greenstar 2000

• Price, inc install (guide): £2,675

• Warranty: 7 years

• Energy efficiency: A rated (93%)

• Power output: 30 kW

• Water flow rate: 10.8 L per minute

• Size: 724 mm (h) x 400 mm (w) x 300 mm (d)

The Worcester Bosch Greenstar 2000 is designed for homes that need a reputable combi in a compact format.

It is often considered where quiet running and smaller spaces matter.

The flow rate is lower than some models on this list, so it tends to suit homes with more modest hot water demand.

Expert opinion: This model earns its place for smaller to medium homes because it offers a compact footprint and a well known platform, but it is best suited to households that do not need especially high hot water flow.

4. Vaillant EcoFIT Pure

• Price, inc install (guide): £3,020

• Warranty: 10 years

• Energy efficiency: A rated (94%)

• Power output: 30 kW

• Water flow rate: 12.2 L per minute

• Size: 700 mm (h) x 390 mm (w) x 295 mm (d)

The Vaillant ecoFIT Pure is a strong option if you want smart control compatibility and steady performance.

With the right controls, features such as weather compensation can help the boiler adjust output more smoothly as outside conditions change.

Expert opinion: We rank it because the flow rate is strong for many homes, the footprint suits lots of installs, and the combination of warranty coverage and control compatibility makes it a sensible modern combi choice.

5. Viessmann Vitodens 100-W

• Price, inc install (guide): £3,125

• Warranty: 12 years

• Energy efficiency: A rated (94%)

• Power output: 30 kW

• Water flow rate: 12.5 L per minute

• Size: 700 mm (h) x 400 mm (w) x 350 mm (d)

The Viessmann Vitodens 100-W stands out for longer warranty coverage and a strong hot water flow rate on paper. It can suit medium to larger homes, but space checks are important because it is deeper than some cupboard friendly options.

Expert opinion: We rate it highly because the 12 year warranty coverage is one of the longest in this shortlist and the flow rate supports higher hot water demand, but you need to confirm space, pipework, and servicing access.

Quick combi comparison table

Use this table to shortlist quickly, then confirm sizing and fit with your installer.

Guide only. Always confirm manufacturer clearances and servicing access requirements before purchase.

Cupboard fit and clearances

If you are planning to fit a combi boiler in a kitchen cupboard, dimensions alone are not enough.

Also consider:

• pipework space below and to the sides

• where the condensate pipe will run

• the flue route and any bends required

• access to service panels for maintenance

• manufacturer clearances for the exact model

Do not block airflow or service panels just to make a boiler fit. If a unit is squeezed in too tightly, it can make servicing harder and can increase the chance of issues later.

Honorable mentions

These models can also be strong choices, depending on your home.

Ideal Logic2 Plus
Viessmann Vitodens 050-W
Worcester Bosch Greenstar CDi Compact
Vaillant ecoTEC Plus

How to choose which combi boiler you need

Step 1 check your hot water demand

If you typically use one shower at a time and do not often run multiple hot taps together, a combi can be a good fit.

If you regularly use hot water in more than one place at the same time, check flow rate carefully and consider whether another boiler type would suit better.

Step 2 match output to your home

kW output is about suitability, not quality.

As a rough guide:

• smaller flats and small houses often suit around 24 to 28 kW

• many typical homes suit around 28 to 32 kW

• larger homes, or homes with higher demand, may need higher outputs, or a different boiler type

Your installer should confirm the right output based on your property, radiator demand, and heat loss.

Step 3 compare warranty coverage properly

Warranty length is easy to compare. Warranty coverage is the part that protects you if something goes wrong.

Before choosing, check:

• what is covered, parts and labour

• servicing requirements to keep the warranty valid

• any exclusions that may matter

Most warranties require annual servicing, and missing this can affect warranty coverage.

Step 4 confirm cupboard fit safely

Do not choose a boiler using dimensions alone.

Also check:

• servicing clearance around the boiler

• pipework space

• the flue route

• where the condensate pipe will run

If a cupboard install is tight, it is often better to change the model than force a poor fit.

When a combi boiler might not be the best option

A combi is not always the right fit.

A system boiler may suit better if you have multiple bathrooms with regular simultaneous use, weak mains pressure, or you want stored hot water for higher peak demand.

Getting a combi boiler quote with iHeat

If you want to check suitability and pricing quickly:

Step 1 get a new combi boiler quote in 60 seconds
Step 2 select the model that suits your home and hot water demand
Step 3 book installation and let the team handle the rest

Finance options may be available, subject to status and eligibility.

Get a quote