Best Combi Boilers 2026: Our Picks for Every Budget, With Fitted Prices

There's no single best combi boiler. The right one depends on your budget, how much hot water you use, and how long a warranty you want. All the big brands make reliable, efficient boilers, so the real differences are price, warranty length, hot water flow and size.

These are our picks from the combi boilers we install, with our fixed fitted prices. We only include boilers we fit, so this isn't a list of every boiler on the market. Prices were correct in October 2026; your exact price is confirmed in your online quote.

Every boiler here is an A-rated condensing gas combi from a major manufacturer with UK parts and support. We compared them on four things that make a real difference day to day:

• Warranty: how long the manufacturer's warranty lasts. This varies from 5 to 12 years across the boilers we fit.
• Hot water flow: how many litres of hot water a minute it can deliver. Higher flow means a stronger shower.
• Size: whether it fits in a kitchen cupboard.
• Price: the fixed price fully fitted, not just the boiler.

As the name suggests, the Compact is small. At 626mm high and 400mm wide, it's one of the smallest combis available and is designed to fit in a kitchen cupboard. It has a stainless steel heat exchanger and is made in Belper, Derbyshire. Glow-worm is part of the same group as Vaillant.

• Outputs: 24kW and 28kW
• Warranty: 5 years
• Fitted price: from £1,799

Best for: a straightforward swap on a tight budget. See Glow-worm boilers

Viessmann is a German manufacturer known for build quality. The 050-W is its entry-level combi, but it still uses Viessmann's stainless steel Inox-Radial heat exchanger, and with us it comes with a 10-year warranty for a little over £2,300.

• Outputs: 25kW and 30kW
• Warranty: 10 years
• Fitted price: from £2,330

Best for: anyone who wants a long warranty without paying premium prices. See Viessmann boilers

The Baxi 800 ticks every box. It comes in three outputs, so there's a size for most homes, and Baxi says it fits a standard kitchen cupboard (it needs just 290mm of depth). It has a stainless steel heat exchanger. The 10-year warranty is conditional on a magnetic filter being fitted and registered with the boiler, which we include.

• Outputs: 24kW, 30kW and 36kW
• Warranty: 10 years
• Fitted price: from £2,600

Best for: most homes. See Baxi boilers

The Vitodens 100-W is the boiler we install with the longest warranty: 12 years. Its stainless steel Inox-Radial heat exchanger is designed so condensate runs off downwards, which helps keep it clean. It's slightly deeper than most combis, so check your cupboard space.

• Outputs: 26kW, 30kW and 35kW
• Warranty: 12 years
• Fitted price: from £2,895

Best for: peace of mind over the long term. See Viessmann boilers

If several taps or showers are often used at once, a higher-output combi helps keep the flow up, as long as your mains water supply can keep up too. The Greenstar 8000+ goes up to 50kW, the highest output we fit, delivering about 20 litres of hot water a minute at that size. It has a colour touch display.

• Outputs: 32kW, 36kW, 40kW and 50kW
• Warranty: 10 years
• Fitted price: from £3,130

Best for: homes with high hot water demand and good mains water flow. See Worcester Bosch boilers

Most boilers are hidden in a cupboard. The Greenstar 8000+ Style is designed to be seen, with a gloss black finish and a colour touch display. Inside, it's the same as the standard 8000+.

• Outputs: 32kW and 36kW
• Warranty: 10 years
• Fitted price: from £3,230

Best for: boilers on show in a kitchen or utility room. Compare the Greenstar range

Prices include the boiler, removal of your old one, a system flush, controls set-up and installation by a Gas Safe registered engineer. Prices correct in October 2026.

For a combi, the kW figure mostly decides how quickly it can heat water for your taps and shower. Bigger isn't automatically better: an oversized boiler costs more to buy and can switch on and off more often. As a rough guide:

If you have three or more bathrooms, or several people often shower at the same time, a combi may not keep up. A system boiler with a hot water cylinder is usually the better choice. Our guide to combi vs system boilers explains the difference.

Long warranties nearly always come with conditions. The most common are:

• registering the boiler with the manufacturer soon after it's fitted
• fitting a magnetic system filter at the same time
• having the boiler serviced every year by a Gas Safe registered engineer

We register the warranty for you when we fit your boiler. After that, book an annual service to keep it valid.