www.which.co.uk52 | September 2011

We surveyed thousands of Which? members about boilers bought in the

last six years, to reveal the brands that won’t let you down.

While Worcester and Vaillant are the best for reliability, for the second year running Baxi’s reliability is poor. And Potterton, Glow-worm, British Gas and Ideal were rated average for reliability – see p54.

This is the fi rst year we’ve also been able to provide reliability information for oil boilers, which are usually installed when you don’t have access to mains gas. Find out how the main oil brands, Grant and Worcester, compare on p55.

KEEP OR REPLACE?With gas and oil prices rising rapidly, some of you have asked us whether it’s worth replacing your old boiler with a highly-e� cient condensing one. If you live in a household

MORE FOR YOU Find reviews of more than 100 boilers o� ered by the manufacturers featured in this article. Regardless of the size of your home and your hot water demands, fi nd the right model for you at www.which.co.uk/boilerssept

that has low to medium gas usage (which equates to between 11,000-16,500kWh per year), it currently doesn’t make economic sense to replace a boiler that’s working perfectly well.

Replacing an old G-rated gas boiler (less than 70% e� cient) with a new condensing boiler that is more than 88% e� cient could cut your fuel consumption by about a quarter and save up to £225 per year, according to the Energy Saving Trust. But you’d need to be spending at least £900 per year on your gas to achieve that level of saving. The average annual bill is currently £658 for gas.

The average new gas boiler installation costs £2,459, so you’d need to make a saving of £205 during each year of its expected 12-year lifespan for it to pay for itself. The average installation price for a new oil boiler is £3,000. However, the economic argument for

replacing older boilers will become more compelling if fuel prices continue to rise.

OUR RESEARCHIn May and June this year, we asked 5,758 members of our online community, Which? Connect, about their gas or oil condensing boilers; 46% had experienced a fault with a gas or oil boiler installed in the last six years.

Our brand reliability score is based on the proportion of owners who needed to get the boiler repaired. Each brand needs a minimum of 50 responses to be included.

Our customer score is a combination of overall satisfaction, and how likely the owner would be to recommend the brand to a friend. We also list the top fi ve problems with each brand’s boilers that owners told us about.

Our survey revealed that the biggest problem owners have faced has been a frozen condensate pipe – on p54-55 we uncover the causes and the remedies for this problem. And if you do need to call an engineer out to fi x a boiler problem, make sure you read our investigation into boiler servicing on p62 fi rst.

TESTLAB

We reveal the most reliable gas and oil boiler brands, and

those that fail their owners

THE MOSTRELIABLE

BOILERS

MOREFORYOU

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www.which.co.uk September 2011 | 53

More on boiler brandsYou’ll fi nd more detail on each of the boiler brands included in our survey, including who to phone if you have an aftersales query, at www.which.co.uk/boilerbrandsrated

Calculating costsThe average cost of a boiler installation is £2,459, but it can be more or less depending on your requirements. For more on costs, go to www.which.co.uk/buythebestboiler

Boiler e� ciencyYou may need new controls to maximise the e� ciency of a new boiler. We explain room thermostats and thermostatic radiator valves at www.which.co.uk/boilere� ciency

MOST RELIABLE GAS BOILER BRANDS

WORCESTERWhich? brand reliability 75% Which? customer score 79% ABOUT WORCESTER British-based manufacturer Worcester, which is part of the Bosch Group, scored an impressive 75% for reliability in our survey and, at 79%, has the highest Which? customer score. A third of those surveyed have opted for a Worcester boiler – it’s the most popular brand among members.WARRANTY Worcester o� ers an impressive 10-year guarantee on the heat exchangers in its boilers, providing that the installation of the boiler meets strict criteria on sizing and positioning. Otherwise, it o� ers a two-year parts and labour warranty.PRODUCT RANGE Worcester o� ers four types of combination boilers (that supply heat and instant hot water). The Greenstar Junior series is the basic range for fl ats and one-bathroom properties. The Greenstar Si series is for slightly larger properties and o� ers a higher hot water fl ow rate. The premium Greenstar CDi range can cope with properties with two bathrooms and provides fl ow rates of up to 17.2 litres per minute.

The Greenstar Highfl ow CDi series includes fl oorstanding combis for large properties.

For homes with a traditional heat- only boiler (those

that use a cold water tank and hot water cylinder for the hot water supply) Worcester o� ers the Greenstar Ri series that can be installed in a cabinet. The higher-powered CDi boilers are for larger properties. The FS CDi regular are for properties where wall-mounting is not feasible.

The compact Greenstar 12i to 24i series and larger 30CDi system boilers provide a range of outputs for homes that use this type of boiler.

MOST COMMON PROBLEMS

■ Problem with built-in controls■ Boiler keeps switching itself o� ■ Water leaking from the boiler■ Boiler completely breaks down■ Boiler noisy in operation

Boilers bought since 1 April 2005. Brand reliability sample size: 567; Customer score sample size: 575; Problems sample size: 144

VAILLANTWhich? brand reliability 75% Which? customer score 77% ABOUT VAILLANT German brand Vaillant shares top place for reliability with a score of 75%, and it also receives a strong endorsement from owners with a customer score of 77%. It’s the second most common gas boiler brand among Which? members – owned by 17% of those surveyed.WARRANTY Typically supplied with a two-year parts and labour warranty (providing the boiler has been serviced 12 months after installation). PRODUCT RANGE Vaillant o� ers four types of combination boiler that supply heat and instant hot water. The range starts with the basic Ecotec Pro which is suitable for smaller homes. The Ecotec Plus range comes in three power levels – the more hot water taps you have the higher the power you will need. The Ecotec Plus 937 is what is known as a ‘storage combi’ – it includes a small storage tank that can store 15 litres of hot water. This reduces the time it takes to deliver piping hot water to your taps, so you don’t have the normal combi time lag between turning the hot

water tap on, and waiting for the hot water to come out. The top-of-the-range Ecotec Exclusive is suitable for larger properties and comes with a

three-year warranty.Vaillant also o� ers an Ecotec

Plus open-vent boiler – the type for homes that have the more traditional plumbing arrangement of a cold water supply tank and hot water storage cylinder. This is available in four heat outputs to cater for small, medium and larger homes.

The Ecotec Plus system boiler provides an even wider range of outputs (12-37kW) for homes that use this type of boiler.

BAXI Which? brand reliability 67% Which? customer score 64% ABOUT BAXI Baxi is a British manufacturer founded in 1866, and now part of the multinational BDR Thermea group along with Potterton and Main. Only 8% of members on Which? Connect with a gas boiler opted for Baxi, and 52% of them had experienced

faults in the last six years.WARRANTY Most ranges are supplied with a two-year parts and labour warranty. This is conditional

on warranty registration and the boiler receiving an annual service.

PRODUCT RANGE Baxi o� ers several combi boiler ranges; the Duo-Tec, Neta-Tec and Platinum. It also produces the Baxi Solo heat-only boiler range, the Baxi Bermuda back boiler range, and the Baxi Megafl o system boiler range suitable for homes with high hot water demands.

Several of the Baxi ranges were updated in summer 2011.

MOST COMMON PROBLEMS

■ Water leaking from the boiler■ Problem with built-in controls■ Boiler noisy in operation■ Boiler keeps switching itself o� ■ Boiler completely breaks down

Boilers bought since 1 April 2005. Brand reliability sample size: 301; Customer score sample size: 304; Problems sample size: 59

LEAST RELIABLE GAS BOILER BRAND

MOST COMMON PROBLEMS

■ Problem with built-in controls■ Boiler keeps switching itself o� ■ Water leaking from the boiler■ Boiler completely broken down■ Boiler noisy in operation

Boilers bought since 1 April 2005. Brand reliability sample size: 132; Customer score sample size: 136; Problems sample size: 62

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www.which.co.uk54 | September 2011

BRITISH GAS Which? brand reliability 71%Which? customer score 69%ABOUT BRITISH GAS British Gas own-brand boilers were developed by manufacturers including Worcester and Glow-worm with input from British Gas. WARRANTY One or two years depending on the manufacturer.PRODUCT RANGE■ One combi boiler range■ Heat-only boiler range – unusually the British Gas 330+ boiler is not available in a range of heat outputs. A single unit is adjusted to suit heat requirements. COMMON PROBLEMS We didn’t receive enough responses from those with a British gas boiler to calculate the most common faults.

GLOW-WORMWhich? brand reliability 71%Which? customer score 69%ABOUT GLOW-WORM British manufacturer founded in 1934; now part of the Vaillant Group.WARRANTY Most ranges are supplied with a two-year parts and labour warranty, although conditions apply.PRODUCT RANGE ■ Three combi boiler ranges ■ Two heat-only boiler ranges■ Two system boiler ranges and a storage system boiler

POTTERTONWhich? brand reliability 71%Which? customer score 68%ABOUT POTTERTON British manufacturer founded in 1850; now part of the multinational BDR Thermea group.WARRANTY Most ranges are supplied with a one or two-year parts and labour warranty, although conditions apply.PRODUCT RANGE ■ Four combi boiler ranges■ Three heat-only boiler ranges■ Two system boiler ranges

IDEALWhich? brand reliability 69%Which? customer score 52%ABOUT IDEAL Founded in 1905, Ideal boilers are still made in the UK.WARRANTY Usually two or fi ve-year parts and labour, subject to product registration and regular servicing.PRODUCT RANGE ■ Three combi boiler ranges■ Four heat-only boiler ranges, including one fl oor-standing model■ Two system boiler ranges

BOILER RELIABILITYKEEP WARM THIS WINTER WITH OUR ADVICE ON HOW TO AVOID A COMMON COLD WEATHER PROBLEM

TESTLAB

GAS BOILER BRANDS WITH AVERAGE RELIABILITY

MOST COMMON PROBLEMS ■ Boiler keeps switching itself o� ■ Problem with built-in controls■ Boiler completely broke down■ Problem with the burner■ Water leaking from the boilerBoilers bought since 1 April 2005. Brand reliability sample size: 165; Customer score sample size: 167; Problems sample size: 53

MOST COMMON PROBLEMS ■ Boiler keeps switching itself o� ■ Problem with the burner■ Problem with built-in controls■ Water leaking from the boiler■ Boiler completely broke downBoilers bought since 1 April 2005. Brand reliability sample size: 96; Customer score sample size: 100; Problems sample size: 46

MOST COMMON PROBLEMS■ Problem with built-in controls■ Boiler completely broke down■ Problem with the burner■ Water leaking from the boiler■ Boiler noisy in operationBoilers bought since 1 April 2005. Brand reliability sample size: 97; Customer score sample size: 99; Problems sample size: 46

YOUR BOILER QUESTIONS

Q Which boiler do I need?Most suitable for replacing installations in

older homes Open vent heat-only. This is the old-fashioned type that works with a cold water feeder tank and a hot water cylinder. Comes in a wide range of heat outputs. Ideal for people who don’t want to radically update their plumbing. Most suitable for space-pressed family homes that use a lot of hot water System boilers – the modern version of a heat-only boiler. They include some of the elements of a traditional open-vent system (often a pump and expansion space) but still store hot water in a cylinder.

Best for flats or smaller houses with limited space and low demand for hot water Combi boiler. Produces hot water on demand by heating it straight from the cold water mains supply.

Q Why do modern boilers switch off in freezing weather?

In our survey, 11% of Which? members with a gas or oil boiler up to six years old reported that their condensate run-o� pipe was frozen.

When the condensate pipe – which drains an acidic liquid from the boiler – becomes blocked with ice, the boiler may shut down to prevent damage.

Ensuring the condensate pipe is at minimal risk of freezing is the responsibility of the boiler installer. The Heat and Hot Water Industry Council

(HHIC) has issued some new recommendations on pipe installation, which include putting the boiler where it can drain into an internal waste pipe; making sure the pipe runs down and away from the boiler and treating pipes going through unheated spaces (ie lofts or garages) as if they are external pipes (see our tips, opposite).

Most problems occur where the condensate pipe is exposed to freezing conditions outside. These problems can be avoided if the pipe is at least 32mm in diameter; takes a short, direct and vertical route to the drain (with no horizontal sections); is completely smooth on the inside (no jagged bits where it was cut down), and is fully insulated from inside the house and down its entire length.

Boilers bought since 1 April 2005. Brand reliability sample size: 97; Customer score sample size: 100; Problems sample size: n/a

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www.which.co.uk September 2011 | 55

Recommended installerOn Which? Local you can fi nd 570 gas installers recommended by other members. Go to www.local.which.co.uk and register or log in to search for those nearest you.

Forum adviceVisit the Which? Local forum at www.local.which.co.uk where topic discussions range from the cheapest way to heat your home to tactics for getting your condensate pipe fi xed.

Extended warrantiesMost boiler manufacturers o� er extended warranties or servicing contracts. Compare their prices against energy company rivals at www.which.co.uk/servicingcontracts

OIL BOILER BRANDS RATED

1 Measure your condensate discharge pipe. If it is less

than 32mm in diameter call a plumber in to replace it. Cost Ask three professionals to quote.

2 Check for sags. Pipes that dip or run horizontally can

allow water to gather and freeze. Clip sagging pipes back into place. Cost Under £7 for 20 waste pipe clips; a DIY job.

3 Simplify the run. Swap complicated pipe runs with

lots of bends for the shortest, most vertical run to the drain.

This task is best tackled by a professional. Cost Get three quotes for comparison.

4 Insulate pipework. Lag the entire external run of

exposed pipes with suitable waterproof and weatherproof insulation. Cost From £8 per metre; a DIY job.

5 Look into ‘trace heating’. If you’ve su� ered frozen

condensate pipes several times, see whether it is possible to install a proprietary trace heating kit with an external frost thermostat.

These kits warm the pipe up in cold weather to prevent freezing. You’ll need to plug most kits into a power socket. Cost Kits cost from £65 depending on the length of pipe; a DIY job.

If all else fails and you have a boiler ‘lock-out’ due to a frozen pipe, use warm (not hot) water, a hot water bottle or self-activating heat pad (like those used to treat back pain) to defrost the blockage on pipes at ground level. Once the blockage is clear, restart the boiler with the reset button.

TAKE ACTION – FIVE TIPS FOR AVOIDING A FROZEN CONDENSATE PIPE

GRANTWhich? brand reliability 72%Which? customer score 75%ABOUT GRANT Grant, based in Devizes, Wiltshire, is largely known for its oil boilers, but is working towards making it easier for homeowners to integrate renewable energy components into their oil-fi red home heating systems. In our survey, 35% of Which? members with an oil boiler had a Grant.WARRANTY A fi ve-year heat exchanger warranty, provided your boiler is installed in accordance with Grant’s instructions, and a two-year warranty for all other components.OIL PRODUCT RANGE Grant produces two main ranges of oil-fi red boilers, the Vortex Pro and the Vortex Eco, with a variety of specifi cations giving fl exibility in where they can be installed.

The Vortex Pro combi boilers are available as internal and external units in three heat outputs, for small to medium homes.

The Vortex Pro range of kitchen/utility and external module boilers are available

in nine di� erent heat outputs to cater for all sizes of home. Most are heat-only and can be converted into system boilers, using the Grant conversion

kit, but some are also available as system boiler variants.

Most of the Vortex Eco range are heat-only boilers, but they can be changed into system boilers using a Grant conversion kit. The range includes wall-hung and fl oor-standing boilers in three heat outputs for small, medium and larger homes. There are ranges that include boilers for installing indoors, outdoors (in a protective casing) or in a utility room.

MOST COMMON PROBLEMS■ Water leaking from the boiler■ Problem with the burner■ Problem with built-in controls■ Boiler keeps switching itself o� ■ Boiler noisy in operationBoilers bought since 1 April 2005. Brand reliability sample size: 135; Customer score sample size: 137; Problems sample size: 39

WORCESTERWhich? brand reliability 72%Which? customer score 71%ABOUT WORCESTER Worcester has been manufacturing domestic oil-fi red boilers since 1962. It has 30 oil-fi red boilers in its current range to suit di� erent types of home, and for internal and external installation. Nearly a third of those surveyed who had an oil boiler had a Worcester.WARRANTY Usually supplied with a two-year warranty and longer cover of fi ve or ten years for the heat exchanger, depending on the range. Extended cover is conditional on regular servicing.OIL PRODUCT RANGE The Greenstar Heatslave combination boilers are available as fl oor-standing internal or external units in three heat output ranges for smaller homes.

There are three fl oor-standing Greenstar Camray ranges of heat-only boilers for installation in a kitchen, garage or externally; three heat outputs are available to supply a wide range of house sizes. The Greenstar Utility range is

suitable for a utility room or garage. The Greenstar Danesmoor wall-mounted range is more suitable for space-pressed

smaller houses but there is also a fl oor-standing version available. All of the Worcester oil-fi red heat-only boilers can be used alongside Worcester solar panel installations.

The Greenstar Camray range of system boilers can be installed in a kitchen, garage or externally; three heat outputs are available for di� erent sized houses and, like the heat-only boilers, can be used with the Worcester Greenskies solar water heating range.

MOST COMMON PROBLEMS

■ Problem with the burner■ Boiler keeps switching itself o� ■ Boiler completely broken down■ Water leaking from the boiler■ Boiler noisy in operationBoilers bought since 1 April 2005. Brand reliability sample size: 118; Customer score sample size: 120; Problems sample size: 51

Horizontal pipes can freeze in cold weather

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