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System boiler guide 2020 | We compare prices on 64 boiler models

07/06/2020

 

What is a system boiler? Who offers the best system boiler prices in 2020?

System boilers commonly work with unvented hot water cylinders and are usually found in modern homes with multiple bathrooms. Prices range from £580 for an entry-level boiler to £1,600 for a premium model. They can also be a good replacement for heat only boilers and work with standard cylinders or combi boilers where you need better hot water performance. The best system boiler for you will be based on your property size and your budget. In this guide we compare prices, sizes, efficiencies and warranties on 64 models of system boiler from nine leading manufacturers, including Worcester Bosch, Baxi, Ideal and Vaillant.

Overview of system boilers

What is a system boiler?

A system boiler provides heating and works with a steel cylinder to provide hot water. System boilers are usually found in larger homes with multiple bathrooms

Find your best system boiler

Use the tables below to find your best boiler based on price, efficiency and warranty length. For example, similar priced boilers offer 2 and 5 year warranties; it's easy to see which one is better value!

Found your boiler? What's next?

Get an estimate of installation cost with our Boiler Quote Calculator. Are you looking for flexible ways to pay for a new boiler? Read our comprehensive guide: 

 

Find your best system boiler

Use the tables below to find your best system boiler. The tables are arranged so that you can easily find your property size and then find who offers the best boiler package for your budget. The tables show boiler performance alongside warranty period and price so you can find the best value boiler. Most boiler manufacturers produce one or two models of system boiler with outputs between 12kW and 40kW. At the smaller end, the price difference between the budget and premium models is quite small. However the disparity grows significantly for the larger models.

Even 'the best' combi boiler is not A-rated out of the box

Combi boilers are not A-rated out of the box, they require a competent installer to set them up correctly and 99% of installers have not been trained to do this. Whilst we guide you on best buys and best performance, they will only fulfil their potential if fitted by an installer trained in correct heating system design principles. Find out more about our work to deliver A-rated heating systems at our Heating Heroes page.

Best buys and best performance

We have identified ‘best buys’ in each size group. These reflect an all-round great package. We have also highlighted best performance boilers, which are not necessarily the cheapest but offer great efficiencies and warranties.

Sizing your system boiler

Most boilers are oversized for the homes they serve. The average UK home requires just 6-8kW of heat on a very cold day. The most popular system boiler is 15-18kW, more than twice the capacity most homes will ever need. So what is wrong with oversizing, just in case?

  • Firstly the boiler will cycle on and off more than it was ever designed to, accelerating wear and tear.
  • Secondly it will rarely operate at its most efficient, i.e. in 'condensing mode', because the return temperatures to the boiler will be too hot. Condensing boilers need the temperature of the water as it flows back to the boiler to be 50 degrees C or less. This requires a correctly sized boiler AND a perfectly balanced system with TRVs that signal the boiler to reduce its output further (modulate) as each room gets warm enough.

The good news is that most modern boilers can be 'ranged rated' down, i.e. the output reduced to more closely match your property's heat requirement, which is calculated by the attending engineer. Make sure you check that the engineer has done this. For more see our Guide to Boiler Sizing.

NOTE In many cases you will require a larger boiler however based on the capacity of your hot water cylinder coil. Coils (like an element in a kettle) may need 12kW or 25kW, depending on their size. The attending engineer will be able to assist with sizing for your hot water requirements.

Guide to using the boiler tables

In the example table below, it is easy to see that the Vaillant ecoTEC plus at £772 is great value with a 7-10 year guarantee, compared the next cheapest and next most expensive, which only offer a 2 year warranty.

1-2 bed flat   Price Standard warranty Free extended warranty Maximum heating output Minimum heating output
Glow Worm System 12 £690.00 7 7 12 4.5
Vaillant ecoFIT pure system

 

612 £865.00 2 7 12 4.7

 

Find your property size and open up the table to find your best system boiler.

1-3 bed properties, small hot water cylinders

As outlined above, the average UK home needs 6-8kW of heat at peak times. It is not currently possible to buy a 6-8kW boiler, the smallest heat only boiler available is 12kW, but you will likely need around 12kW of capacity to heat a small hot water cylinder in a reasonable amount of time. Your hot water requirements will be determined by the attending engineer.

Boiler Model Price Standard warranty Free extended warranty Maximum heating output Minimum heating output
Ravenheat CS system boiler 24 £546 2 2 26 4.0
Glow Worm System 12 £690 7 7 12 4.5
Vaillant ecoFIT pure system 612 £865 2 7 12 4.7
Worcester Bosch Greenstar System i 12 £900 5 10 12 3.1
Ideal Vogue System 15 £905 10 10 15 3.2
Vaillant ecoTEC plus system

612 £910 5 10 12 3.3
Worcester Bosch Greenstar 8000 30 30 £1,310 5 10 30 3.0
Viessmann 200-W System

11 £1,375 2 5 11 1.9

 

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Hero Support

With our years of experience and research, we get you the best boiler package for an efficient, long-lasting boiler

 

2-5 bed houses, larger hot water cylinder

If you have a larger hot water cylinder then you will need a larger output boiler. As boiler sizes increase however, so does the lowest minimum output. The best boilers are those that can go down really low (see right hand column) whilst still providing enough capacity for a bigger hot water cylinder. The most expensive boiler is the most efficient - amazing work by Worcester Bosch. However the best buys go to Vaillant and Ideal for a great price and guarantee period on the boiler

Boiler Model Price Standard warranty Free extended warranty Maximum heating output Minimum heating output
Ravenheat CS system boiler 24 £546 2 2 26 4.0
Glow Worm Energy System 15 £715 7 7 15 4.5
Ideal Logic System 15 £765 2 2 15 5.1
Ideal Logic + System 15 £795 7 7 15 5.1
Ideal Vogue System S15 £905 10 10 15 3.2
Baxi System 615 £905 7 7 16 4.9
Vaillant ecoFIT pure system 615 £925 2 7 15 4.7
Worcester Bosch Greenstar System i 15 £950 5 10 15 4.6
Vaillant ecoTEC plus system

615 £960 5 10 15 3.3
Worcester Bosch Greenstar 8000 30

30 £1,310 5 10 30 3.0
Viessmann 200-W System 19 £1,310 2 5 19 1.9

 

3-5 bed houses, multiple bathrooms

Here we see Potterton and Ferroli enter the group offering two incredible cheap boiler models and the Ferroli comes with a 5 year warranty. Viessmann still offers the best efficiencies in the pack. NB ignore that some boilers have much larger maximum outputs than others - the important figure is how low the boiler will go (right-hand column).

Boiler Model Price Standard warranty Free extended warranty Maximum heating output Minimum heating output
Ravenheat CS system boiler 24 £546 2 2 26 4.0
Potterton Gold System 18 £590 2 2 18 4.2
Ferroli Modena HE 18S 18 £600 5 5 17 4.3
Intergas HRE

18 £789 7 7 18 5.6
Glow Worm Energy System 18 £795 7 7 18 5.0
Ideal Logic System 18 £805 2 2 18 5.1
Ideal Logic + System 18 £895 7 7 18 5.1
Baxi System 618 £930 7 7 19 4.9
Ideal Vogue System 18 £985 10 10 18 3.9
Vaillant ecoFIT pure system 18 £1,000 2 7 18 5.1
Viessmann 100-W System 19 £1,035 5 10 19 4.3
Worcester Bosch Greenstar System i 18i £1,050 5 10 18 4.6
Vaillant ecoTEC plus system 18 £1,080 5 10 18 4.1
Worcester Bosch Greenstar 8000 30 30 £1,310 5 10 30 3.0
Viessmann 200-W System 19 £1,310 2 5 19 1.9

 

3-5 bed houses, multiple bathrooms + very large hot water cylinder

You will only need a 25kW boiler for high hot water demand households. Prices at the top end of this group are almost three times that of the entry level boilers. The Ideal Logic + System is a great all-round buy for larger hot water requirements whilst the Viessmann 200-W provides the ultimate efficiencies. Both Ravenheats are amazing value, although warranty periods are slightly shorter.

Boiler Model Price Standard warranty Free extended warranty Maximum heating output Minimum heating output
Ravenheat CS system boiler 24 £546 2 2 26 4.0
Ferroli Modena HE 25S 25 £605 5 5 25 6.2
Potterton Gold System 24 £615 2 2 24 6.8
Main System Eco Elite 24 £617 3 3 26 8.3
Ravenheat HE System 98S £649 5 5 25 3.7
Glow Worm Energy System 25 £845 7 7 25 6.1
Ideal Logic System 24 £850 2 2 24 5.1
Ideal Logic + System 24 £860 7 7 24 5.1
Intergas HRE 24 £869 7 7 23 7.2
Intergas HRE 30 £949 7 7 27 7.6
Baxi System 624 £1,015 7 7 25 4.9
Worcester Bosch Greenstar System i 24i £1,060 5 10 24 7.2
Worcester Bosch Greenstar System i 27i £1,070 5 10 27 7.0
Viessmann 100-W System 26 £1,095 5 10 26 4.3
Ideal Vogue System 26 £1,110 10 10 26 5.6
Vaillant ecoFIT pure system 625 £1,150 2 7 25 6.4
Vaillant ecoTEC plus system 624 £1,225 5 10 24 5.7
Vaillant ecoTEC exclusive 27 £1,345 5 10 26 4.2
Worcester Bosch Greenstar 8000 30 30 £1,310 5 10 30 3.0
Viessmann 200-W System

25 £1,465 3 10 25 1.9

 

Priority domestic hot water systems

Very few homes need 30kW for heating, but large homes with multiple bathrooms in use simultaneously may need a 30kW boiler of if your engineer can set the system as as priority domestic hotwater. The lower end boilers are plentiful but only the Ferroli offers a decent 5-year warranty. The Viessmann represents great value and great efficiency standards.

Boiler Model Price Standard warranty Free extended warranty Maximum heating output Minimum heating output
Potterton Gold System 28 £794.00 2 2 28 10.2
Glow Worm Energy System 30 £833.00 2 7 30 7.5
Ideal Logic System 30 £883.00 2 2 30 6.4

Ideal Logic + System

30 £902.00 7 7 30 6.4
Viessmann 100-W System 30 £1,070.00 5 10 30 9.1
Worcester Bosch Greenstar System i 30i £1,105.00 5 10 30 7.0
Ideal Vogue System 32 £1,187.00 8 10 32 6.8
Vaillant ecoFIT pure system 630 £1,212.00 2 7 32 7.5
Vaillant ecoTEC plus system 630 £1,308.00 5 10 32 6.4
Worcester Bosch Greenstar 8000 30 30 £1,310.00 5 10 30 3.0
Viessmann 200-W System

30 £1,545.00 3 10 30 1.9

 

Boiler Model Price Standard warranty Free extended warranty Maximum heating output Minimum heating output
Potterton Promax System 32 £948.00 2 2 34 9.4
Worcester Bosch 8000 35 £1,352.00 5 10 35 3.5
Vaillant EcoTEC Plus System 37 £1,312.00 5 10 37 7.1
Viessmann 100-W System 35 £1,511.00 5 5 35 5.4
Viessmann 200-W System 35 £1,571.00 5 5 35 1.9

 

What is a system boiler?

System boilers work with a steel unvented hot water tank. They are usually found in larger properties with multiple bathrooms as they can supply good hot water flow rates simultaneously to two or more outlets (e.g. two showers). Unlike heat only boilers, all of the components that would usually be found external to the boiler (pumps, valves etc) are inside a system boiler. This means more of the heating system is covered by the boiler manufacturer's warranty. System boilers require good incoming water pressure and good internal flow rates to operate at their stated capacity. If you currently have a heat only boiler on a gravity system you will need to check your water flow rates to make sure a system boiler will work.

When is a system boiler right for my home?

System boilers suit properties with multiple bathrooms, particularly where they are in use simultaneously, for example people showering in the morning. System boilers provide good hot water flow rates from a high performance cylinder. Many new build properties have system boilers with unvented hot water systems, replacing your boiler will be a straight swap. For those considering installing a system boiler in place of their combi boiler, this is worth while when you are extending and adding bathrooms. You will need to find a spot for the hot water tank and preferably close to the bathrooms. For those with a conventional heat only boiler, you will need to change the boiler and the copper cylinder.

 

Jo Alsop

Heating Hero

The Heating Hub

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