The best combi boilers in 2026, ranked by the engineers who fit them
Originally published 27 January 2020. Rewritten 21 September 2026 with the boilers we fit today, the prices we actually charge, and the sizing rules our engineers use at a survey.
Every brand says it makes the best combi boiler. Every comparison site ranks them differently. After more than thirty years of fitting and repairing boilers across Yorkshire, our view is simpler: the best combi boiler is the one that is sized correctly for your home, fitted by an installer accredited for that brand, and registered for the full manufacturer warranty. Get those three right and any of the boilers below will serve you well. Get them wrong and the badge on the front will not save you.
Here is what we would put in our own houses, and why.
The short answer
| Boiler | Best for | Combi outputs | Warranty with BASI | Fitted from |
|---|---|---|---|---|
| Worcester Bosch Greenstar 4000 | The all-rounder for one and two bathroom homes | 25kW, 30kW | Up to 10 years | £1,895 |
| Vaillant ecoTEC plus | Larger homes, quiet running, the longest cover | 26kW, 32kW, 36kW, 40kW | Up to 10 years | £2,095 |
| Ideal Logic | Value, landlords and smaller homes | 24kW to 35kW | 2 years standard, 10 years on the Logic Max | £1,695 |
Every price is a fully fitted figure with the system flush, magnetic filter, thermostat and old boiler disposal included, fixed in writing after a 20 minute survey. There is no “starts from” small print, because the survey is what sets the price.
1. Worcester Bosch Greenstar 4000, the all-rounder
The Greenstar is the boiler we fit most, and the 4000 is the model most Yorkshire homes end up with. Worcester Bosch describe it as designed for small to medium homes with a bathroom, and that is exactly where it belongs: two and three bedroom houses with one bathroom, or a second bathroom that is not in constant use.
It comes in two outputs. The 25kW delivers around 10.5 litres of hot water a minute and the 30kW around 12.3, while the central heating output of both sits at roughly 24kW. In practice that means the choice between them is about how fast you want a bath to fill and how often two hot taps run together, not about how many radiators you have.
Build quality and parts support are the draw. Worcester Bosch has the densest dealer and spares network in the country, so a warranty call-out is quick and a part is rarely more than a day away. As Worcester Bosch accredited installers, our registered installs carry up to a 10 year manufacturer warranty, which is what most fitters cannot offer on the same boiler. Supplied and fitted from £1,895.
2. Vaillant ecoTEC plus, the long-warranty pick for bigger homes
The ecoTEC plus is the quieter of the two premium boilers and the one we reach for when the house is larger or the hot water demand is higher. The current combi range runs from 26kW through 32kW and 36kW to 40kW, so it scales from a three bedroom semi with two bathrooms right up to a large family house without moving to a system boiler and cylinder.
Vaillant use a stainless steel heat exchanger where Worcester Bosch use aluminium silicon. Both are proven; stainless is marginally more tolerant of poor water quality and the ecoTEC tends to be a fraction more efficient, which is worth having in a hard water part of Yorkshire. We are Vaillant Advance installers, so a registered ecoTEC install carries up to a 10 year guarantee. Fitted from £2,095.
If you are weighing the two premium brands against each other, our Worcester Bosch vs Vaillant comparison goes through the real differences in price, noise, heat exchanger and warranty side by side.
3. Ideal Logic, the value pick
The Logic is the boiler we recommend when the budget is the deciding factor and the home is a typical two to three bedroom house. It is a straightforward, dependable A-rated combi, cheap to look after because parts are plentiful, and popular with landlords for exactly that reason. We supply and fit the Ideal Logic combi from £1,695, the lowest installed price on this page, with a 2 year manufacturer warranty on the standard model.
Ideal also make the Logic Max in 24kW, 30kW and 35kW versions, which carries a 10 year manufacturer warranty at a higher price. If you want the Ideal name with the longer cover, ask at the survey and we will price both.
What about Viessmann, Baxi, Alpha and the rest?
We service and repair every major make: Baxi, Glow-worm, Viessmann, Potterton, Ferroli, Alpha and the others. Owning one is not a problem, and our Baxi service and repair page covers the questions we get most about that brand. Several of them make a perfectly good boiler.
When we choose what to fit new, though, we stay with the three ranges above, and the reason is the warranty rather than the boiler. We are accredited for Worcester Bosch and Vaillant, which is what unlocks the 10 year cover, and we know the Logic inside out. A cheaper headline boiler from a brand we are not accredited for usually comes with a shorter warranty, and the number that matters is the total cost over the life of the boiler, not the day-one price.
What size combi boiler do I need?
This is the question that actually decides whether you are happy with your boiler, and it is the one most comparison sites skip. On a combi the hot water demand sets the output, not the number of radiators. A second bathroom matters far more than a fourth bedroom.
As a rule of thumb:
| Your home | Combi output |
|---|---|
| 1 to 2 bedroom flat or terrace, 1 bathroom | 24kW to 26kW |
| 3 bedrooms, 1 bathroom | 24kW to 30kW |
| 3 bedrooms, 2 bathrooms | 30kW to 32kW |
| 4 bedrooms, 2 bathrooms | 32kW to 36kW |
| 4 to 5 bedrooms, 3 bathrooms | 36kW to 40kW, or a system boiler with a cylinder |
Two things move a home up or down that table. The first is mains water pressure and flow: a combi can only heat the water that arrives, so a house on a weak supply will not get the flow the boiler is rated for whatever output you buy. The second is how many outlets run at once. A combi serves one hot tap well and two poorly; if two showers run every morning, a system boiler with a cylinder is the better answer and we will say so. Our combi vs system boiler guide covers that choice properly.
We measure the pressure and flow at the survey, count the bathrooms and radiators, and only then name a model. Nobody should be sold a 40kW combi for a two bedroom flat, and it happens more than you would think.
25kW or 30kW?
Neither is better. The 30kW fills a bath faster and copes with a family bathroom in constant use; the 25kW is right for a smaller home with one bathroom where the extra output would never be used, and it is a little cheaper. The heating side of both is about the same, so the radiators are not the deciding factor.
How many radiators will a 30kW combi run?
More than almost any house has. The heating output of a 30kW combi is usually around 24kW, and a typical radiator needs one to two kilowatts, so it comfortably runs 12 to 15 radiators. If you are choosing a combi by radiator count, choose it by bathrooms instead.
Which combi boilers should you avoid?
We get asked for a blacklist and we do not keep one. Every brand has made a poor boiler at some point and every brand makes a decent one now. What we would avoid is not a badge but a set of mistakes:
- A boiler with no UK parts network. A cheap import that needs a part from abroad is a cold house for a fortnight in January.
- A short warranty on a premium price. Five years should be the floor on anything over £2,000 fitted; ten is available on the right boiler with the right installer.
- An install by a fitter who is not accredited for that brand. The boiler is the same; the warranty is not.
- Buying on output alone. An oversized combi short-cycles and wastes gas. An undersized one struggles on a winter morning with two showers running.
Avoid those four and the brand question becomes a matter of budget and preference rather than risk.
What about efficiency?
Every boiler on this page is A-rated under the ErP energy label, and the difference in seasonal efficiency between the top brands is small enough that you would never see it on a bill. What you will see on a bill is how the boiler is run. A combi set to a 60 degree flow temperature with a decent thermostat and thermostatic radiator valves uses noticeably less gas than the same boiler left at its factory setting. Our guide to reducing your gas bill in winter starts with that one change, and getting control of your heating covers the controls that make the most of a modern boiler.
Why a combi at all?
For most one to three bedroom homes a combi is the right type of boiler, and it is now the most common type installed in the UK. It heats your radiators and gives you hot water on demand from one unit, so there is no cylinder in the airing cupboard and no tank in the loft. You only heat the water you use, the hot water arrives at mains pressure so a shower is strong without a pump, and the install is simpler and cheaper than a system boiler because there is less to fit.
The trade-offs are real but specific. A combi struggles to serve two hot outlets at once, which is the reason larger households with several bathrooms are better with a cylinder. An existing power shower may need adjusting or replacing, because a combi already delivers mains pressure. And like any boiler it wants an annual service to keep the warranty valid and the breakdowns away.
What you pay, and what is included
Our installed prices are fixed figures, not “from” figures. The Ideal Logic from £1,695, the Greenstar from £1,895 and the ecoTEC plus from £2,095 each include the survey, the system flush, a magnetic filter, a thermostat, removal of the old boiler and the first year’s service. Nationally a mid-range combi runs roughly £2,000 to £2,800 installed, so those prices sit at the sensible end without anything left out. What moves the figure is the size of boiler, where the flue and pipework are, and whether you are switching type, all of which is covered in our new boiler cost in Yorkshire guide. Finance is available from £23 a month subject to status, with a soft credit check that does not affect your score.
Get it sized and priced for your home
The 60 second fixed-price quote tells you what your home needs, surveyed and priced with no salesman and no “starts from”. We fit all three ranges every week from our Leeds Road base, so if you are local start with boiler installation in Bradford or a new boiler in Leeds for the fixed prices in your town.
Common questions
Which combi boiler is the best in 2026? For most UK homes we rank the Worcester Bosch Greenstar 4000 first as the all-rounder, the Vaillant ecoTEC plus first for larger homes and the longest cover, and the Ideal Logic first on value. The best one for you is the one sized correctly, fitted by an accredited installer and registered for the full warranty.
Which combi boiler is the most reliable? Worcester Bosch and Vaillant sit at the top of independent reliability surveys. In our experience sizing, a proper flush and filter at install, and an annual service matter more than the brand.
Which combi boilers should I avoid? No brand blacklist. Avoid a boiler with no UK parts network, a short warranty on a premium price, an install by a fitter not accredited for that brand, and buying on output alone without a survey.
What size combi boiler do I need for a 3 bedroom house? With one bathroom, 24 to 30kW. With two bathrooms, 30 to 32kW. Hot water demand and mains pressure set it, which is why we measure at the survey.
Is a 25kW or 30kW combi better? Neither. On the Greenstar 4000 the 25kW gives around 10.5 litres a minute of hot water and the 30kW around 12.3, with a similar heating output. Choose by bathrooms and bath-filling patience.
How many radiators will a 30kW combi run? Around 12 to 15, because the heating side is roughly 24kW and a radiator needs one to two kilowatts. That covers almost every three or four bedroom house.
How much does the best combi boiler cost installed? With BASI, from £1,695 for the Ideal Logic, £1,895 for the Greenstar and £2,095 for the ecoTEC plus, fully fitted and fixed after a survey. Nationally, roughly £2,000 to £2,800 for a mid-range combi.