Which is the best boiler brand?
The makers' guarantees side by side, and what else to weigh.
Calls answered 24 hours a day
- Best boiler brands: the guarantees compared
- The most reliable boiler: who measures it
- All our engineers are Gas Safe registered
Makes we repair
Is one make the best? The short answer
No one boiler brand is the best for every home. None of the makers' or official pages read for this guide names one. Your Gas Safe registered engineer can advise on the best gas boiler for you and your home. The best make for a home is one whose range suits it, from a maker whose guarantee terms you can keep. It should be fitted and serviced as that maker asks.
Efficiency differs less from make to make. Every new gas boiler fitted in an existing home in England has to reach the same minimum, save in exceptional circumstances. Which? found the makers' efficiency claims generally accurate in its earlier tests.
The makes our engineers fit most are Vaillant and Worcester Bosch. A boiler we fit gets the maker's own magnetic filter where its guarantee asks for one. Ring us on 020 8064 0067 for a quote, from photos of your old boiler or after a free survey visit.
The guarantee, and what it asks
A maker's guarantee runs from 2 years to 12 or more, by make and range. The longest ask the most of you:
- the maker's own filter
- an installer in the maker's scheme
- registration within 30 days
- a service every year
The list below gives twelve makers' terms, make by make.
The installer
The installer decides a lot of what a make delivers. A gas boiler must be fitted by a Gas Safe registered installer, and the longest guarantees at several makers depend on who fits the boiler. Which? says a boiler's performance depends heavily on the system it is connected to, and how it is installed.
The range for your home
The type and the size come before the make, and each maker aims its ranges at different homes, from flats to the largest family homes. Combi, system or regular, and which suits which home.
The parts and the repairs
Repairs under a guarantee go to the maker, and its terms can set rules for the parts. Vaillant's guarantee ends if non-genuine parts are used in a repair.
Sources: Gas Safe Register and Which?.
How the main makes differ
The main boiler makes differ most in their guarantees, in how long each one lasts and what the longest ask of you. Here are twelve makers' terms, as read at each maker's own page on 12 October 2026, in alphabetical order. Each make's name links to its page here, with its models and fault codes. Terms change, and differ from model to model. The papers that came with a boiler say which apply to it.
Alpha
Standard guarantee
7 years on the E-Tec NX, and 10 on the E-Tec Plus NX
Longest offered
13 years, on the E-Tec Plus NX
What the longest asks for
Alpha's PremierPack Pro. 11 years with its Cyclone Plus NX filter on its own
Ariston
Standard guarantee
Up to 8 years on the Clas ONE family and 5 on the E-Combi ONE family. 2 if you register the boiler yourself
Longest offered
Up to 12 years, on the Genus ONE Net and Alteas ONE Net
What the longest asks for
A Smart Protect maintenance contract with the installer, paid to the installer, with yearly maintenance. Without one, those two have up to 2 years
ATAG
Standard guarantee
12 years
Longest offered
18 years, and a lifetime replacement guarantee on the heat exchanger
What the longest asks for
A code from the installer for the 18 years. Some parts have shorter terms, and products sold before 2025 may have shorter ones
Baxi
Standard guarantee
2 years on the 200 range, 5 on the 400, 7 on the 600 and 10 on the 800
Longest offered
10 years, on the 800
What the longest asks for
The 800's magnetic filter, fitted and kept up for the whole term
Glow-worm
Standard guarantee
2 years on the Micracom to 7 on the Energy
Longest offered
10 years, on the Energy and the Ultimate
What the longest asks for
A Glow-worm Power System Filter, registered through Club Energy, its installer scheme
Ideal
Standard guarantee
2 years on the Logic Heat and Mexico HE. 7 on the Logic+, with 10 on its heat exchanger. 10 on the Logic Max and Vogue Gen2
Longest offered
12 years, on the Vogue Max
What the longest asks for
A MAX accredited installer
Intergas
Standard guarantee
3 years on the Rapid, 6 on the Rapid Plus, 7 on the HRE, 10 on the Eco RF, Xclusive and Xtreme
Longest offered
12 years, on the Xclusive
What the longest asks for
An Intergas System Filter, fitted with the boiler
Navien
Standard guarantee
12 years, on the NCB700
Longest offered
12 years
What the longest asks for
Not given on the product page we read
Vaillant
Standard guarantee
2 years on the ecoTEC pro, and 5 on the ecoTEC plus
Longest offered
10 years
What the longest asks for
On the ecoTEC plus, a myREWARDS installer, registered with Vaillant's Boiler Protection Kit or Advanced Boiler Protection Kit, a filter. On the ecoTEC pro, an upgrade that may be charged for
Viessmann
Standard guarantee
2 years if the boiler isn't registered. 7 for many boilers registered within 30 days
Longest offered
Longer, by a paid extension
What the longest asks for
Registration and the extension, through the installer
Vokera
Standard guarantee
5 years on the Easi-Heat i to 12 on the Pinnacle
Longest offered
12 years, on the Pinnacle
What the longest asks for
Not given on the page we read
Worcester Bosch
Standard guarantee
5 to 8 years, by range: 5 on the Greenstar 1000 and 7 on the 2000, each with a system filter. 8 on the 8000+
Longest offered
12 years on the Greenstar 8000+. 10 on the 4000, CDi Compact, i System Compact, 8000 F and Ri
What the longest asks for
A Greenstar System Filter, not the System Filter Micro, fitted by a Worcester Bosch Accredited Installer or Accredited Partner
The longest guarantees ask the most of you:
- a maker's own filter: Worcester Bosch, Vaillant, Baxi's 800, Glow-worm, Alpha and Intergas
- an installer in the maker's own scheme: Worcester Bosch, Vaillant, Glow-worm, Ideal, ATAG and Ariston
- a paid extension or contract: Viessmann, Vaillant's ecoTEC pro and Ariston
Most of these makers' terms also ask for the boiler to be registered within 30 days of fitting. If it isn't, the guarantee falls back to a shorter one. They ask for a service every year too.
What six makers' guarantees ask for every year.
Every make we repair, current and discontinued, and the groups behind them.
Sources: each maker's own guarantee page and terms, read on 12 October 2026.
Worth knowing
A new boiler's guarantee keeps its full length once the boiler is registered with its maker within 30 days of fitting. If it isn't, Vaillant, Ideal and Intergas cut theirs to 12 months, and Ariston and Baxi to a year.
Which is the most reliable boiler?
No maker's page or official body read for this guide names one make as the most reliable boiler. Which? scores boiler brands on reliability from its own surveys, but keeps the scores for its members. That's why this page gives none.
Which? asks boiler owners every year. In May 2025 it asked more than 10,000 people with a boiler fitted in the previous six years whether it had needed a repair. A brand's reliability score is the share of its boilers repaired in that time, adjusted for their ages. It counts how soon the first fault came and how serious it was, from at least 50 owners a brand.
Which? also asks heating engineers, 225 of its Trusted Trader engineers, leaving out any paid by a maker to recommend it. It asks them about:
- build quality
- how easy a common fault is to fix
- how easy the parts are to get
- servicing
- the support for installers
Which?'s overall score weighs reliability and the engineers' views most.
- Maintenance: boilers can be very reliable and long-lasting if they are properly maintained. The makers' guarantees ask for a service every year.
- Clean water in the system: Vaillant charges for a visit when a failure comes from dirty system water, such as sludge or limescale. ATAG asks for the system to be cleaned to the standard BS 7593, and kept free of sludge.
- A guarantee isn't a reliability score: a guarantee is the maker's promise of a repair, with free parts and labour, or a replacement. It applies when the boiler breaks down from a fault in its materials or its fitting, as Ideal describes its own. Its length shows the terms, not how often a make goes wrong.
A yearly boiler service, and what it includes.
Sources: Which?, on how it assesses boilers and Gas Safe Register.
Which make suits which home
The make that suits a home comes after the type and the size. The makers sell their ranges as combis, system boilers and regular boilers in a spread of outputs. Ideal's Logic Max and Ariston's Clas ONE family are examples. Vokera's ranges each come as a combi and a system boiler. Within a type, each maker aims its ranges at a kind of home, in its own words:
Worcester Bosch: the Greenstar ranges
Worcester Bosch aims its Greenstar 4000 at small to medium homes with one bathroom. It makes its Greenstar CDi Compact to fit inside a kitchen cupboard, with the power for a busy home with two bathrooms. It designed its Greenstar 8000+ for the largest family homes.
Vaillant: the ecoTEC pro and ecoTEC plus
Vaillant aims its ecoTEC pro combi at small to medium homes that want hot water on demand with no tank. Its ecoTEC plus range includes a 40kW store model, for homes that use a lot of hot water.
Viessmann: the Vitodens 050-W and storage combis
Viessmann says its Vitodens 050-W suits smaller homes and flats. It says storage combis suit households that use a lot of hot water. They keep a store of hot water inside a combi, with no separate cylinder.
Navien: the NCB700
Navien sells its NCB700 combi as able to give hot water to three bathrooms at the same time, and gives it a 12-year guarantee.
Glow-worm: regular boilers
Glow-worm says its regular boilers suit larger households with several bathrooms and a high demand for hot water. They suit homes with low water pressure or older radiators too.
Ideal: the Logic Max in each type
Ideal makes its Logic Max as a combi, a system boiler and a regular boiler. They're the Logic Max Combi, System and Heat, so the one range comes in the type a home needs.
The home picks the type and the size, and several makers offer a range to suit it. The guarantee terms you can keep may decide between them.
What a repair engineer looks at
A boiler's make, model and guarantee shape its repair. The model, on the boiler's data plate, says which parts fit. While the maker's guarantee runs, the maker or its authorised engineer repairs a manufacturing defect. The makers' own terms set out the rest.
While the guarantee runs
A boiler under its maker's guarantee goes to the maker for a manufacturing defect. Vaillant's terms and Glow-worm's page say the maker or its authorised engineer repairs it. Vaillant won't pay another firm's bill unless it agreed in writing beforehand. Ring the maker while the guarantee runs. Once it has ended, or for a fault it doesn't cover, ring us any time.
Genuine parts
The parts fitted in a repair can affect the guarantee. Vaillant's ends if non-genuine spare parts are used in any repair. ATAG's terms leave out unauthorised work on its products.
The jobs left to you
Topping up the pressure, bleeding air and thawing a frozen condensate pipe are the owner's own jobs in Vaillant's terms. Its guarantee doesn't pay for them, and Vaillant suggests a Gas Safe registered engineer for them.
Parts with terms of their own
Some parts carry shorter terms than the boiler. ATAG's terms give its internal expansion vessel five years, its ignition electrodes and burner gasket kit two, and its flue parts one. The boiler has twelve.
Parts for older boilers
Parts for a discontinued boiler are found by its model, wherever they are still available. The brands page sets out which makes are discontinued, and how long one maker aims to support its parts. Discontinued boiler makes, and their parts.
When you ring us
A call about a repair starts with the make and the model. We'll ask for both when you ring, and whether the boiler is still under guarantee. The rate is agreed in writing before any repair starts. How a boiler repair visit goes.
Choosing a new boiler? We fit every make and model, and quote from photos of your old boiler or after a free survey visit. Having a new boiler fitted, and what the price includes.
Do you cover my part of London?
Yes: we fit and repair boilers of every main make all over Greater London, in every borough north and south of the Thames. Pick your side of the river to see the areas.
North of the river
Every borough north of the Thames: Barnet and Enfield at the top, Hillingdon in the west, Havering in the east, and central London in between.
South of the river
Every borough south of the Thames: Richmond and Kingston in the west, Bexley in the east, and down through Croydon to Sutton and Bromley.
Questions about choosing a make
Which make has the longest guarantee?
ATAG's guarantee is the longest on the makers' pages read for this guide on 12 October 2026. It's 12 years as standard, and 18 years through a code from the installer. That needs the boiler registered within 30 days and serviced every year, with its water checked. ATAG's heat exchanger has a lifetime replacement guarantee, and some of its parts have shorter terms. Alpha's E-Tec Plus NX reaches 13 years with its PremierPack Pro. 12 years are offered on Worcester Bosch's Greenstar 8000+, Ideal's Vogue Max, Intergas's Xclusive, Vokera's Pinnacle, Ariston's Genus and Alteas ONE Net, and Navien's NCB700. Each is on its maker's terms. The longest terms ask the most of you, as the list shows.
Are cheaper boilers worth buying?
A cheaper boiler from a maker's entry range usually comes with a shorter standard guarantee than its top range. Weigh the guarantee as well as the price. Baxi's 200 has two years against its 800's ten, and Vaillant's ecoTEC pro two against the ecoTEC plus's five. Ideal's Logic Heat has two against the Logic Max's ten, and Glow-worm's Micracom two against its Energy's seven. Intergas's Rapid has three against its Xclusive's ten. Worcester Bosch's Greenstar 1000 has five, with a system filter, against the 8000+'s eight. Every new gas boiler fitted in an existing home in England reaches the same minimum efficiency. Which? expects little difference in gas use between the most and the least efficient. What a new boiler's price includes.
Does the installer matter more than the make?
The installer matters as much as the make, and decides a lot of what the make delivers. A gas boiler must be fitted by a Gas Safe registered installer. The longest guarantees at Worcester Bosch, Vaillant, Glow-worm, Ideal, ATAG and Ariston depend on who fits the boiler. Baxi's terms have the installer complete the Benchmark checklist. Which? says a boiler's performance depends heavily on the system it is connected to, and how it is installed. The right size comes from a heat loss calculation. What to look for before a new boiler goes in.
Which type and size should I buy?
The type and the size come before the make. The type comes from the hot water the home uses at once, its water pressure and its space. The size comes from the heat the home loses, and the hot water it uses. Combi, system or regular, and which suits which home. How the size of a boiler is worked out.
Don't know what has failed? You don't have to.Ring and say what you can see or hear. Finding the fault is our job.
Calls answered 24 hours a day
A real person answers and gives you the rate on the call. No work starts until you say yes, and repairs are guaranteed for 12 months: parts, labour and any return visit.
