Best gas boilers 2021 | Our 'Pepsi Challenge'

 

Which is the best gas boiler for my home?

We have undertaken a fully independent review of the vast majority of domestic gas boilers available to buy in the UK. Most 'best buy' blogs are written by boiler installation companies and are biased in favour of the boilers sold by that company. Even Which? do not assess the technical merits of the boiler, relying rather on customer service criteria and market opinions, not technical facts. This means consumers never get a clear view of which is actually the best boiler for them and their budget.

We are completely independent and impartial with no affiliations with boiler manufacturers. Our assessment of UK boilers is based first and foremost on the technical merits of the boiler. We did the 'Pepsi challenge' for boilers, which is not to say we were  blindfolded, thankfully, rather we ignored brand strength, marketing blurb and the number of boilers sold. 

Our discovery

Following our review, we have found that the UK boiler market is made up of what we have termed 'low-tech' and 'high-tech' boilers. Low-tech boilers present few options for adjusting the boiler to your heating system to make it run efficiently whilst high-tech boilers offer the latest technology and the most potential to run efficiently.

Our most surprising discovery however is that price is absolutely no indication of whether a boiler is low-tech or high-tech. We found some very expensive low-tech boilers from familiar brands and very cheap high-tech boilers from manufacturers you may never of heard of.

Warning label

We want to answer the question of 'which is the best boiler' honestly and provide some meaningful advice on this topic. But our recommendations come with some heavy caveats and warning labels, as follows:

1) A boiler is only as good as the installer that fits it.

2) A boiler is only as good as the heating control it is paired with.

So that even 'the best' boiler will perform poorly if setup incorrectly and paired with a basic control. 99% of installers have not been trained to setup condensing boilers to run at their A-rated efficiencies and basic controls are not banned under building regulations, so most boilers are B-E rated in the home. (You can find out more about our work to recruit the top 1% of installers and shortlist high efficiency controls with the right boilers, go to Expert Panel.)

Award summary

We have grouped together boilers by type (combi, heat-only and system boilers) and then grouped them again by price. The tables show the boilers we have reviewed and the winners are given for each section. 

Best heat only boilers

1. Vaillant EcoFit Pure
2. Worcester 8000
3. Glow Worm Energy

Best system boiler

1. Viessmann 200
2. Ravenheat CS
3. Intergas Xclusiv

Best combi boilers

1. Ravenheat HE80
2. Intergas Xclusive and Vaillant EcoTec Pure
3. Viessmann Vitodens 200

The best combi boilers

In the tables below we have presented the smallest combi boilers in each range, by which we mean with the lowest hot water performance. Larger boilers that give a better hot water performance are available in all models but remember that the higher hot water performance, the less efficient they tend to be for heating. If you need a combi with a big hot water performance see the section at the end of this page.

 

The best entry level combi boiler - WINNER! Ravenheat HE80

As well as a great price and very decent 5-year warranty, the most impressive aspect of this boiler is its minimum output. All boilers operate within a range of maximum and minimum outputs. The lower the boiler can go the more efficient it will operate all year round. To find a boiler for this price that can operate at 3.9kW is very impressive!

Manufacturer/Model	Code	Price	Standard warranty	Free Extended Warranty	Max heating output	Min heating output	Litres per minute hot water
Main Eco Elite	25	£525	5	5	24kW	8.4kW	10.2
Ideal Independent	24	£670	5	5	24kW	4.8kW	9.9
Alpha Evoke	28	£670	3	7	27kW	4.3kW	12.1
Ravenheat HE80	25	£649	5	5	21kW	3.9kW	10.2
Potterton Titanium	24	£715	7	7	21kW	7.4kW	9.8
Glow Worm Energy	25	£700	3	3	19kW	5.3kW	10.1

 

The best mid-range boiler - JOINT WINNERS! Intergas Xclusive and Vaillant Ecotec Plus

This is a crazy category. Prices vary between £738 at the lower end and £1,145, with no real consistent explanation as to the price difference. The cheapest and the second most expensive have the same lower output on the boiler – 7.4kW – the same efficiencies and the same hot water performance. Only the warranty is longer on the Baxi Platinum.

The winners are two great all-rounders. The Intergas Xclusive and Vaillant Ecotec Plus. The Intergas is a great price with a 10-year warranty. The Intergas has the edge with a lower minimum output and coupled with their sophisticated controls it is one of the most efficient boilers on the market. Vaillant are a more familiar brand with a strong customer service back up. Remember, the lower the boiler can go, the more efficiently it can operate all year round.

Manufacturer/Model	Code	Price	Standard warranty	Free Extended Warranty	Max heating output	Min heating output	Litres per minute hot water
Potterton/Titanium	24	£715	7	7	21kW	7.4kW	9.8
Worcester 2000	25	£778	5	10	20kW	6.7kW	10.0
Ideal Logic Plus	C24	£825	7	7	25kW	7.1kW	9.9
Vaillant Ecofit Pure	825	£910	2	7	19kW	5.3kW	10.4
Baxi Ecoblue Advance	24	£1,020	10	10	21kW	4.9kW	9.8
Intergas Xclusive	24	£969	10	10	19kW	3.6kW	9.8
Worcester Greenstar Si	25	£1,045	5	10	24kW	8.1kW	9.8
Ideal Vogue	C26	£1,005	10	10	19kW	4kW	10.6
Viessmann	100-W	£1,070	5	7	26kW	4.7kW	8.9
Baxi Platinum	24	£1,110	10	10	24kW	7.4kW	9.8
Vaillant Ecotec Plus	825	£1,145	5	10	20kW	3.8kW	10.5

 

Best high-end combi boiler - WINNER! Viessmann Vitodens 200-W

At the upper end we have the ground breaking Viessmann 200 boiler. With the lowest output on the market at an impressive 1.9kW, this is one of the most efficient boiler available to buy.

We’d also like to give a special mention to the Intergas Xtreme. Still impressive at 3.6kW at the lower end and the cheapest of the group, this is an incredible boiler with some of the most advanced heating controls available.

Manufacturer/Model	Code	Price	Standard warranty	Free Extended Warranty	Max heat output	Min heat output	Litres per minute hot water
Intergas Xtreme	24	£1,209	7	7	20kW	3.6kW	11
Intergas Xclusive	30	£1,029	10	10	23kW	3.6kW	12.2
Worcester 8000	30	£1,275	5	10	30kW	3kW	10.7
Viessmann Vitodens 200	W	£1602	3	10	25kW	1.9kW	15.7
Vaillant ecoTEC Green iQ	835	£1,465	5	10	26kW	3.4kW	14.5

 

 

The best heat only boilers

We have researched the majority of heat only boilers to bring you our pick of the best priced and best-performing heat only boilers for 1-3 bed houses and larger homes. REMEMBER, the vast majority of UK homes do not need anything bigger than a 6-8kW boiler, 10kW max! Most of us will need a boiler from the 1-3 bedroom table, but you must factor in hot water production.

Best heat only boiler for 1-3 bedroom properties

The average UK home does not require more than 6-8kW of heat on a very cold day. Therefore the smallest boilers available to buy (commonly 12-13kW) will comfortably heat most homes. The most important figure to note in the tables below is not the maximum capacity – which will always be enough – but the lowest capacity. The lower the minimum output the more efficient the boiler will operate all year round.

REMEMBER - the hot water must be set up correctly for smaller output boilers. Smaller boilers will take longer to heat up a cylinder of water and that must be factored in. If you have a 12kW cylinder however then a 12kW boiler will suffice.

If you have a larger hot water cylinder then go to one of the larger models below (also see next table down). The important thing to note is the minimum output of the boiler. The Worcester 8000 has a big output of 30kW but can go right down to 3kW. This will give you 30kW of power for hot water and reduce down to 3kW for the heating.

We have ranked boilers in order of the lowest output. This means that the Worcester 30 boiler, which can output at 30kW, is actually the most efficient for smaller homes; it is also the most expensive. We have given our best boilers based on price and all-round good value:

Boiler	Code	Price	Standard warranty	Free Extended Warranty	Max heating output	Min heating output
Worcester 8000 regular	30	£1,275	5	10	30kW	3.0kW
Worcester Greenstar Ri	12i	£810	5	10	12kW	3.4kW
Vaillant ecoFIT pure regular	412	£740	2	7	12kW	4.5kW
Glow Worm Energy Regular	12	£740	7	7	12kW	4.5kW
Vaillant ecoTEC Plus Regular	412	£805	5	10	12kW	4.5kW
Ideal Logic Heat +	12	£705	7	7	12kW	5.1kW
Intergas HRE	18	£759	10	10	18kW	6.1kW
Viessmans Vitodens 100-W Regular	26	£960	5	5	26kW	7.2kW
Baxi 200	12	£600	3	3	13kW	7.5kW

Best priced heat only winner for 1-3 bed homes - WINNER! Vaillant EcoFIT Pure

A great all-round purchase, particularly when it comes with the 10-year warranty (it must be fitted by an accredited installer to get this).

Best efficiency heat only boiler for 1-3 bed homes - WINNER! Worcester 8000 30kW

A little pricey at £1,253, but it offers the lowest output in the market and with a 10-year warranty.

The best heat only boilers for larger properties

Remember that most properties in the UK need less than 10kW on a very cold day, which includes a lot of larger properties. For example, a 4 bed home will need 4-8kW of heat depending age and insulation levels. For heating systems, the smallest boilers will be sufficient, i.e. 11-13kW, but larger properties are likely to have larger hot water requirements. Therefore you will need to consider a bigger output boiler that goes down really low on the heating side.

Again we have ranked boilers in order of their lowest output and again the Worcester Bosch 8000, a 30kW boiler, has the lowest output, making it the most efficient.

NOTE: It is really important not to increase your boiler size ‘just in case’ as the next size up boiler will have a higher minimum output and this will reduce efficiencies. Only increase the size of the boiler if you need more power for hot water.

Boiler	Code	Price	Standard warranty	Free Extended Warranty	Max heating output	Min heating output
Worcester 8000	30	£1,275	5	10	30kW	3.0kW
Glow Worm Energy Regular	15	£755	7	7	15kW	4.5kW
Vaillant ecoFIT pure regular	415	£775	2	7	15kW	4.5kW
Vaillant ecoTEC plus regular	415	£880	5	10	15kW	4.5kW
Worcester Bosch Greenstar Ri	15	£830	5	10	15kW	4.6kW
Ideal Logic + Heat	15	£740	7	7	15kW	4.9kW
Main Eco Compact	15	£685	5	5	16kW	5.4kW
Intergas HRE	18	£759	7	7	18kW	6.1kW
Viessmans Vitodens 100-W Regular	16	£855	5	5	16kW	7.2kW
Baxi 200 Heat	15	£630	3	3	16kW	7.5kW

Best priced heat only boiler for larger houses - WINNER! Glow Worm Energy

At £722, it’s one of the cheapest and with the second lowest minimum output.

Best efficiency heat only boiler for larger houses - WINNER! Worcester 8000 30kW

Again a pricey £1,253 but it offers the lowest output in the market.

The best system boilers

We have reviewed the technical datasheets of all system boilers to find the most technologically advanced and best value. Again the lower the minimum output the more efficient the boiler will operate all year round. Our research has revealed some surprising winners.

The best system boiler for 1-3 bed houses, small hot water cylinder

All boilers operate within a range of maximum and minimum outputs - the lower the boiler can go the more efficient it will operate all year round. Remember that most UK homes only need 6-8kW on a very cold day, therefore the smallest system boilers available to buy (9kW-12k) will comfortably heat most homes.

However you must factor in hot water requirements. A 12kW boiler will take longer to heat a cylinder than a 30kW boiler. If you need a high output boiler for a large hot water cylinder, pick one that goes down really low on the heating side.

We have reviewed all of the system boilers on the market to bring you boilers with low minimum outputs.

Manufacturer/Model	Code	Price	Standard warranty	Free Extended Warranty	Max heating output	Min heating output
Viessmann Vitodens 200-W	11	£1,375	5	10	11kW	1.9kW
Worcester Greenstar system	9i	£903	5	7-10	9kW	3.0kW
Ideal Vogue system	15	£905	10	10	15kW	3.2kW
Vaillant Ecotec Plus	824	£1,107	2	10	20kW	7.1kW
Baxi System	624	1015	7	7	25kW	4.9kW
Vaillant ecoTEC Plus	612	£910	2	7	12kW	4.7kW
Worcester 8000 system	30	£1,310	5	10	30kW	3.0kW
Ravenheat CS system boiler	24	£545	5	5	26kW	4.0kW
Worcester Greenstar system	12i	900	5	10	12Kw	3.1kW
Vaillant ecoFIT pure	612	£865	2	7	12kW	4.7kW
Glow Worm Energy	12	£690	7	7	12kW	4.5kW
Viessmann Vitodens 100-W	19	£1,035	5	5	19kW	4.3kW
Ideal Logic + system	15	£795	7	7	15kW	5.1kW

Best priced system boiler - WINNER! Ravenheat CS System 24

An incredible low £546 with an impressive 4kW minimum output. A great economy boiler, but just 2 years of warranty cover.

Best efficiency system boiler - WINNER! Viessmann Vitodens 200-W

Viessmann's latest boiler goes down to an incredible 1.9kW at the lower end - the lowest on the market. A little more expensive than the Worcester 8000 but well worth it for the efficiency gains.

Best system boilers for large houses, large hot water cylinder

We have found that many boiler manufacturers do not offer boilers under 15kW, hence why some 15kW or bigger appear in the 1-3 bedroom table above. The important figure to note is the minimum output in the right hand column. If that is low then it will be more efficient all year around.

Remember that most properties in the UK need less than 10kW on a very cold day, which includes a lot of larger properties. For example, a 4 bed home will need 4-8kW of heat depending age and insulation levels. For heating systems, the smallest boilers will be sufficient, i.e. 11-13kW, but larger properties are likely to have larger hot water requirements. Therefore you will need to consider a bigger output boiler that goes down really low on the heating side.

Again we have ranked boilers in order of their lowest output and again the Worcester Bosch 8000, a 30kW boiler, has the lowest output, making it the most efficient.

NOTE: It is really important not to increase your boiler size ‘just in case’ as the next size up boiler will have a higher minimum output and this will reduce efficiencies. Only increase the size of the boiler if you need more power for hot water.

Manufacturer/Model	Code	Price	Standard warranty	Free Extended Warranty	Max heating output	Min heating output
Viessmann Vitodens 200-W	11	£1,470	5	10	19kW	1.9kW
Worcester 8000	30	£1,310	5	10	30kW	3.0kW
Ideal Vogue system	15	£905	10	10	15kW	3.2kW
Ravenheat CS system boiler	24	£546	2	2	26kW	4.0kW
Vaillant ecoFIT pure	612	£865	2	7	12kW	4.7kW
Baxi 600 system	15	£905	7	7	16kW	4.9kW
Worcester Greenstar system	12i	£900	5	10	12Kw	3.1kW
Viessmann Vitodens 100-W	19	£1,035	5	10	19kW	4.3kW
Ideal Logic + system	15	£905	10	10	15kW	3.2kW

Best prices system boiler for larger homes WINNER! Ravenheat CS System 24

Very low price of £546 with an impressive 4kW minimum output. A great economy boiler, but on 2 years of warranty cover.

Best efficiency system boiler for larger homes WINNER! Viessmann Vitodens 200-W

Incredible low minimum output of 1.9kW making it efficient all year round.

The best combis for big hot water performance

We have reviewed all the big hot water combis and compared them against their lowest outputs for heating. If you have two or more bathroom in use simultaneously then some of the larger combis may meet your requirements.

The downside of some larger combis is that the minimum heat requirement increases as the hot water performance increases.

It is essential that the boiler is not oversized as they are almost all too big for UK homes. Many 2-3 bathroom homes still only need 6-10kW of heat on a very cold day. Make sure the boiler’s maximum output is reduced down to meet this. We celebrate the manufacturers that have achieved great hot water flow rates alongside low minimum outputs. The top four on our table are all high-performance, high efficiency combis. Pair with a compensation control to achieve the best possible efficiencies.

Best combi for hot water WITH low minimum output - WINNER Viessmann 200-W

is the clear winner with a low output of 1.9kW and flow rate of 15.7 litres per minute. Although at the upper end price wise.

Best priced combi for hot water WITH low minimum output - WINNER! Intergas Xtreme

A decent low output and at the lower end price wise. The heating controls for Intergas are amongst the most efficient on the market so you would definitely benefit from further fuel savings with this boiler.

Manufacturer/Model	Code	Price	Standard warranty	Free Extended Warranty	Max heating output	Min heating output	Litres per minute hot water
Viessmann Vitoden 200	25	£1,602	3	5	25kW	1.9kW	15.7
Worcester 8000	45	1,904	5	10	34kW	3.5kW	16.1
Intergas Xtreme	36	£1,389	7	7	27kW	3.6kW	14.5
Vaillant ecoTEC Green iQ	843	£1,688	>5	10	33kW	4.3kW	17.8
Ideal Vogue	40	£1,318	10	10	34kW	6.1kW	16.4
Baxi Ecoblue advance	40	£1,364	5	5	34kW	8.4kW	16.4
Baxi Platinum	40	£1,328	5	5	34kW	12.1kW	16.4