When it comes to needing a new boiler it is important to choose a manufacturer that produces highly efficient and reliable products, with an excellent quality heat exchanger, a suitable control system and good modulation ratios. Making the right choices at this stage of the installation will help ensure your new boiler will run as efficiently as possible whilst suiting your individual needs and living a long and happy life performing well.
However, the most common question we find in heating is “what do you think of ‘brand x’. The problem here is that each manufacturer has ranges, you can't assume all the range from 1 manufacturer is better or worse than another. For example, you can't compare an entry-level boiler range built on price for one manufacturer, to a top range from another and assume that holds for all the rest of their offerings!
So What are you comparing? High end? Low end? You can't compare a combination boiler to a heat-only boiler! Here's a quick look into each manufacturer's range and a quick overview.
This boiler is a heat-only wall-mounted gas-fired condensing boiler. It's small and compact enough to fit in a standard kitchen cupboard or other areas where space is limited. It has rated outputs of 11 kW, 16 kW, 19 kW, 25 kW and 32 kW and an ERP efficiency rating of 93%, which puts it in the class A bracket. A large user display on the front of the boiler with weather compensation controls available. This boiler comes with a standard 5-year warranty. This boiler is suitable for most residential properties throughout the UK. The advantage of most heat only boilers is that there's nothing in them to go wrong, they are very basic boxes, the downside is that they have very little technological improvements and typically incredibly poor modulation ratios, read more on that here.
The advantage here is how small the unit is, making it an easy cupboard fit, including the latest version.
The 100 range is their mid-range offering. Like the heat only version, this boiler is efficient, compact, quiet and reliable. With outputs available from 3.2 kW to 32 kW this boiler is a good choice for smaller and well-insulated homes. Thanks to a low-speed fan it's also quiet during operation. The heat exchanger is high-quality stainless steel offering great efficiency, performance and a long lifespan. Able to convert up to 94% of the fuel used into heat this makes this boiler highly efficient and like the heat, only version is class A-rated for energy efficiency. A large user-friendly LED touchscreen for easy operation is mounted on the front of the boiler. Equipped with Lambda Pro combustion control technology the flame is constantly monitored to maintain a nice clean and efficient burn. Wifi is built into the boiler interface as standard, allowing the heating system to connect to the internet if required. With the choice of advanced weather compensation or load compensation control, you can select a control strategy that suits your individual requirements. As standard, this boiler comes with a 5-year warranty, with the option to extend by a further 7 years. This boiler is also hydrogen ready (H2 20% blend) for the future.
The Vitodens 111-W is a high-performance hydrogen ready wall mounted storage combination boiler for family homes with a high demand for hot water. Using a cylinder loading system and 46 litres integrated internally mounted stainless steel storage tank this model is capable of running multiple showers at once, provided the cold water supply is sufficient. Available in outputs 3.2 kW to 32 kW this boiler can suit most residential homes. Boasting a high hot water flow rate of 18 litres a minute and more this hot water performance is the equivalent to a separate 150-litre unvented cylinder. The LED touchscreen is used on this model as is the case with all Viessmann boilers, with the same options for controlling the system as well. This model also fits in the class A bracket for ErP efficiency and comes standard with a 5-year warranty with the option to extend by another 7 years. 20% blend) for the future.
The 050 is Viessmann entry level-affordable range and only available as a combination boiler. A small compact combination boiler that can fit inside a standard kitchen cupboard. Like most boilers in the Viessmann range, this model also has a high-grade stainless steel heat exchanger. The domestic hot water output can be range rated from 3,2 to 30 kW, allowing hot water flow rates at the outlets up to 12 litres per minute. At a slightly lower ErP energy rating of 92% this model is only a fraction less efficient overall but still falls inside the class A band. The same digital interface is mounted on the front of the boiler for easy use. Lambda Pro combustion control is also employed here and this model is also hydrogen ready. Wifi is also included as a standard. With the options of advanced weather compensation or load compensation, you can select the right control strategy for your home and individual needs. This model comes with a warranty of up to 10 years.
This is Viessmann's high-end range. This model is wall-mounted and only 450mm wide. Targeted for the new generation of heating systems, with greater efficiency, lower emissions and ease of operation this boiler is future proof, highly durable and digital. With the same high-grade stainless steel heat exchanger and up to 98% of the fuel being burned being converted to useful heat, this model is the most efficient. Throughout the range, with outputs up to 32 kW. The modulation range on this model is an impressive 17:1. This turndown ratio allows the boiler to modulate down to varying loads with ease and maintain the correct output required where other boilers struggle. More on modulation here.. This particular model has the usual wifi built-in but also has a Vitotronic control unit with a 7-inch colour touchscreen for easy use. This model also fits in the class A bracket for ErP efficiency but in this case, uses the new environmentally responsible MatriX-Plus burner. This burner reduces fuel consumption thanks to the 17:1 modulation range and has automatic combustion control, optimising the burn at all times. This makes this burner a lot cleaner for the environment and produces up to 40% less NOx emissions than other less sophisticated burners. This boiler is hydrogen ready, comes with Viessmann’s standard warranty of 5 years which is extendable to 10 and 12 years and is available in both system boiler and combi boiler models.
With all the technology from the 200 range, this model is a floor standing storage combination boiler with an integral enamelled hot water cylinder to give much higher hot water capacity, as the 111 above, feeding multiple showers at once and giving the equivalent to a 210L unvented cylinder. With the stainless steel heat exchanger and MatriX-Plus burner, this unit boasts greater efficiencies and lower harmful emissions released into the atmosphere, controlled by the highly reliable Lambda Pro combustion controller. Available with outputs from 1.9 kW to 32 kW this model is ideal for domestic properties with large hot water needs. With integrated wi-fi as standard, the 7-inch colour touchscreen and fluorescent light guide displaying correct operation this model is easy to use by the end-user.
The Greenstar range of Worcester gas condensing combination boilers is their top of the range combi’s. With outputs, up to 50 kW these models are suitable for homes of most sizes and capable of supplying two or more bathrooms. Worcester’s entire domestic boiler range uses an efficient aluminium heat exchanger and is ready for hydrogen on a 20% blend. All but one of their gas combi ranges have an A rating in ErP energy efficiency for heating and hot water. There are two colour options for this boiler, either white or black to suit your home. An easy to use colour display mounted on the front of the boiler, with wireless connectivity with their own smart thermostat. An optional intelligent filling system is available upon request. When installed by a Worcester accredited installer the warranty can be extended up to 12 years.
The Greenstar Life range of combi’s is built upon the Greenstar CDi Classic boiler. The new design features an upgraded boiler display screen and controls with push buttons and wireless connectivity making control of your heating and hot water in the home easier. This model is suitable for homes with more than one bathroom and when installed by a Worcester accredited installer can have a warranty of up to 12 years.
The Greenstar CDi Compact combination boiler is suitable for small, medium and large-sized properties with one or two bathrooms. It is compact enough to fit inside a standard kitchen cupboard or other areas with limited space. This model features user-friendly displays for ease of use. The hot water temperature can be adjusted to meet your specific requirements and has simple boiler control knobs with a cleat temperature display. A wide choice of controls are available for comfort and economy and this model has an A+ ErP package efficiency rating for heating when installed with a smart internet-connected Bosch EasyControl. The first protection is included as a standard to prevent freezing when installed in colder areas. Up to a 10-year guarantee is available when installed by a Worcester accredited engineer.
This model is virtually the same as the Greenstar CDi Compact mentioned above. The only real difference is it's designed for smaller properties with no more than one bathroom. This model also can have a warranty of up to 10 years if installed by a Worcester accredited installer.
The Greenstar 4000 is targeted for small and medium-sized homes with only one bathroom. This model has a greater modulating range than other Worcester combi’s. This means it's better suited to match the varying demands throughout the year and reduce fuel consumption. The new modern design comes with an easy to use colour display screen and features wireless connectivity with the Bosch EasyControl system. This model can have a warranty of up to 10 years if installed by a Worcester accredited installer.
The Greenstar 2000 is Worcester’s lowest-priced combination boiler. It's suitable for apartments and small or medium-sized homes with only one bathroom. Compact in size it fits inside or between standard kitchen cupboards. This model features Worcester's Quick Tap water-saving feature. This is activated with a quick open and close of a hot tap. This helps to reduce your water wastage in the home. This model comes with a standard 10-year guarantee on the primary heat exchanger. The rest of the boiler has a standard 5-year warranty or 6 if the system is fitted with a Greenstar system filter at the same time.
The Greenstar CDi Highflow is Worcester’s floor standing storage combination boiler. Designed to fit under standard kitchen worktops this unit is compact and quiet. Larger homes can be supplied with higher output options if needed. This model can supply high hot water flow rates of over 90 litres draw off. On the front of the boiler are simple to control knobs with temperature displays. Frost protection is included as standard on this model as well, so the boiler can be fitted outside of the kitchen in colder areas if needed. A wide choice of control options is available to suit your needs.
The Greenstar Junior combination boiler is Worcester’s low-end budget combi. There are two available outputs, a 24 kW version and a 28 kW. These models are designed for apartments and small to medium size homes with one bathroom. The 24i Junior produces 9.8litres per minute, whereas the 28i produces 11.4 litres per minute. Both these models have an efficiency rating of 90% and above. The controls on these models are very basic compared to other ranges of Worcester boilers and a 2 or 5-year warranty is available. The primary heat exchanger comes with a 10-year guarantee as standard.
The top of the range Style and Life system boilers offer greater outputs and the same connectivity found in their combination boilers. With outputs of up to 50 kW these models are capable of heating homes of most sizes. Available in either black or white options to suit your home. This model has a warranty of up to 12 years if installed by a Worcester accredited installer.
These models come with two available output options. The 27 to 30 kW option is the highest output for the i range. This model is suitable for small, medium and larger homes and can also be fitted in a standard kitchen cupboard. The smaller output model comes in ranges from 9 to 24 kW and is suitable for smaller and medium-sized properties. Both boilers are suitable for homes with unvented cylinders and work well with Greenstore cylinders and Greenskies solar panels for energy savings. Simple control knobs mounted on the front of the boiler and easy to use visual displays are included.
The Greenstar 4000 is ideal for small to medium-sized homes with one bathroom. It features a new modern design and an easy to use full-colour text display screen. With a wide power range, it is capable of covering most domestic needs and helps to reduce gas consumption and lower energy bills. Wireless connectivity with the Bosch EasyControl comes standard like other models. This model can also be used with Greenskies solar panels. A warranty of up to 10 years is available, again if installed by a Worcester accredited installer.
This model offers larger outputs from 50 kW to 100 kW. This boiler is targeted for large domestic and commercial applications. They can be installed on their own or as part of a cascade system. The 50 kW and 100 kW versions are compatible with solar thermal installations
The Greenstar Life is part of Worcester’s most powerful wall hung heat only boiler range. With updated controls and connectivity for modern-day life. This model is suitable for larger properties and with more than one bathroom. A ten-year warranty is possible as well.
This model comes in two available output options as well. The larger model comes with 27 to 30 kW options and the smaller output model 9 to 24 kW, the same as the system boiler versions. Like the system versions, both Ri models are compatible with Worcester’s Greenskies solar thermal panels and as a standard come with frost protection. A 10-year warranty is available as an option for both these models as well.
This model is ideal for replacing original floor-standing boilers. Offering high output options this model can supply the heat in larger buildings. Like the system floor standing version it fits under standard kitchen worktops. Has simple boiler control knobs and temperature display giving clear information on the operation. Suitable for larger homes with a stored hot water cylinder, the hot water recovery time is kept low and is also compatible with the Greenskies solar thermal system.
As mentioned, you cannot judge each boiler manufacturer just by the band. That is to say, you cannot compare a Viessmann 050 boiler (Viessmann low end budget option) to the Worcester 8000 (their high end option) you have to compare range for range.. Also boiler type, we cannot compare Viessmann heat only to a Worcester combi. What does simplify this is that the two brands ranges sit very much in the same price bracket so, assuming this as a constant, let us do this for you:
First, we will take a look at high-end system boilers. Let's take a look at the Viessmann Vitodens 200-W and the Worcester Greenstar 8000 Style. Both offer high-quality products with a range of control options to suit your needs but the similarities stop there. The Viessmann 200-W has output options up to 32 kW but most importantly an impressive modulation ratio of 17:1. Having a good modulation ratio, or turndown ratio enables the boiler to accurately modulate its input to better match varying demands on the system.
If we had the boiler rated at 32 kW with that turndown ratio the burner would be able to modulate down to about 1.9 kW. As the weather warms, or changes in the system occur the boiler will constantly try to adjust its output to match the load. A boiler with a poor modulation ratio will struggle to match the smaller loads, this will cause an increase in gas consumption and can cause cycling of the boiler. Cycling of any burner is not desired. This will put a lot of wear and tear on components each time the boiler starts, eventually leading to premature failure to parts. More on modulation and cycling here.
As opposed to Worcester's Aluminium heat exchangers, Viessmann also uses high-grade stainless steel heat exchangers throughout their entire range. A link below will take you to another article explaining why although aluminium does have some benefits, stainless steel is potentially the best choice for heat exchangers. Efficiencies and reduced harmful emissions are further improved with the use of their MatriX Plus burner and the Lambda Pro combustion control system. As pointed out above this burner can not only convert up to 98% of the burnt fuel into useful heat, it also produces around 40% less NOx emissions. Minimising NOx and other harmful emissions is important to help clean the environment and help safeguard this planet's future.
The Greenstar 8000 Style comes with outputs up to 50 kW but a much smaller turndown ratio of 10:1. Here lie two problems. A boiler of this size would be hugely oversized for the typical homes they're intended for and with poor modulation, they will struggle to match varying loads as the outside temperature drops or zones begin to shut down.
As mentioned above, accurately sizing your heat source and having high modulation ratios is paramount to maximising efficiency, prolonging the life of the boiler and helping the environment.
The other advantage of using a Viessmann system boiler is that they come as ‘4 pipe systems’. Essentially this means they have a built-in diverter valve and controls built-in. Not only does this give better value for money it means they have in-build hot water priority, without getting too technical means you can run your heating at much more optimal temperatures and maximise efficiency. Worcesters offerings will need addons for this which disappointingly comes in 15mm instead of 22mm, slowing heat delivery to the cylinder.
Lastly, the V200 comes with controls built in the front in the form of a very intuitive colour touch-screen display, it isn't necessary to add another control or timer!
Now let's consider each manufacturer's mid-range system boilers. We’re going to compare the Viessmann 100-W and the Worcester Greenstar i. The Viessmann 100-W is available in outputs up to 32 kW and although has a lower modulation ratio of 10:1 like the 200-W, this is still the same as Worcester’s high-end system boiler and in this case still much better than their low-end boiler. The Viessmann 100-W still houses the same high-grade quality stainless steel Inox-Radial heat exchanger as the other models and uses the Lambda Pro combustion control system as well. This low-end model does not have the same MatriX PLus burner as the 200-W but still boasts up to 94% of the fuel being burned to useful heat.
The Greenstar i system boiler has outputs between 9 and 24 kW. However, the turndown ratio on this boiler is about 3:1. As you can see this is not only a poorly modulating boiler but even the Viessmann low-end system boiler is vastly superior at modulating. As mentioned earlier as well, all of Worcester’s domestic range have aluminium heat exchangers.
Again with Viessmann’s 100 system boiler, they come with a built-in control system and come as ‘4 pipe systems’. As described above not only does this give better value for money it means they have in-build hot water priority, which can run your heating at much more optimal temperatures and maximise efficiency.
Another advantage here, however, is that as well as accepting Viessmann’s world-class controls, the Viessmann 100 also speaks open therm! Opening up to 3rd party intelligent modulating controls. Watch choosing smart stat video here
Now let's take a look at each manufacturer’s high-end combination boilers. We will look at the Viessmann 200-W combi and the Greenstar CDi Highflow. The Viessmann comes in two output options targeted for hot water performance. There's a 30 kW option that can provide 12.3 litres per minute of hot water and a 35 kW option producing 14.3 litres per minute. One advantage of these models is it still has the same 17:1 turndown ratio as the system boiler version. This means if the boiler has been sized for hot water performance (which is often the case when sizing combi’s) the burner is still able to modulate down low enough to match low load situations when in heating mode. As with the system boiler version these models use the same MatriX Plus burner and Lambda Pro combustion control.
If high hot water performance is required then the Greenstar CDi Highflow is a good choice. With hot water flow rates of up to 25 litres per minute, this boiler is suitable for larger homes with multiple bathrooms. However, the turndown ratio is about 4:1. This is poor modulation and if the model has been selected primarily for hot water performance could cause lots of cycling issues, especially in warmer months or in well-insulated buildings.
However, for a true comparison, you would probably compare a Vitodense 222. Provided you have a good incoming supply pressure this will produce over 35L per minute! However is floor standing and quite large due to the built-in hot water cylinder.
Now we will take a look at their low-end combination boilers. For Viessmann, we will take the Vitodens 050-W combi and for Worcester the Greenstar 24i Junior. The 050-W is available in several outputs with hot water flow rates between 12.1 and 14.3 litres per minute. However being low-end models their modulation range is a small 4 : 1. The Greenstar is available in two outputs. There’s the 24i which produces 9.8 litres per minute of hot water and the 28i produces 11.4 litres per minute. These models have a turndown ratio of around 3 : 1. As you can see even Viessmann’s low-end combi has slightly better-modulating capabilities than the Worcester but the Viessmann still has the same high-grade stainless steel heat exchanger as every boiler in their range and can use Viessmann’s vast range of superior controls as well as open therm controls!. The Worcester controls are very basic. Compatible with Worcester’s simple mechanical timers and most of their digital programmers and room thermostats, the control options for this low-end boiler are limited and the Viessmann 050 comes with built-in advanced weather compensation and speaks open therm so much better options available or you can use Viessmann controls with Internet control and accepts up to 20% hydrogen mix which the Worcester Junior boilers do not accept.
Finally, we will briefly cover heat only boilers. The thing to note with heat only boilers is there is no high and low end. All heat only is low end. They typically have poor modulation and not much going on inside them. They are built to fit a very specific gap in the dated UK market only.
As such, there is very little to say here. However, another clear winner, the Viessmann breaks the traditional heat only mold has an up-to 1 to 10 modulation, vs Worcester 1 to 4. The 100
Worcester is a bot smaller at 270mm depth as opposed to Viessmans 285mm but there's not much in it. Adding all the above advantages from Viessmann there's not much more to say here.
The 200 range of Viessmann boilers is not currently OpenTherm ready. This range of their boilers uses advanced weather compensation, or older on/off controls if the customer prefers. The 100 range of Viessmann boilers are OpenTherm compatible and uses Viessmann’s own control system also which allows both the 100 and 200 to run much more intelligently to match the load. The 100 range also has the same high quality and performing weather compensation controls built into it as standard, meaning depending on your design requirements you can use either weather compensation, OpenTherm or older on/off control strategies. This is explained a bit more simply in this smart stat video.
Viessmann boilers all have a 5-inch colour touchscreen from the Vitotronic range and come supplied with an outdoor sensor that wires directly into the boiler if using weather compensation. The Vitotronic range all have an energy cockpit built-in for energy analysis and management. This monitoring allows the end-user to see their gas consumption for heating and hot water. If a solar thermal system is also in use this monitors the solar yield and displays this information as well. If used with a Vitocell cylinder the energy cockpit can also provide information on the cylinder loading status, temperature stratification and temperature curves. Furthermore, the Vitotronic can also give detailed information on how much a particular energy source (gas or solar) has contributed to loading the cylinder. Hot water times, hot water circulation and weather compensation heating times and temperatures are all visible and adjustable on the screen. Viessmann also offers external controls like the Vitotrol 200 and 300 which give the end-user the optional solution of supplying a room influence percentage on your weather compensation. An optional Vitoconnect will give the end-user full app control over the boiler and the heating and hot water. Viessmann WiFi module also allows your heating engineer to monitor your system remotely should you wish.
Another huge advantage Viessmann have over Worcester is they have access to the best control system available in the world and simply plug into any other renewable technology you might add in the future.
Worcester Bosch boiler controls are less attractive to Viessmann. Their range uses the EMS protocol system and currently in the UK Worcester is the only known manufacturer to use some form of this system, which means 3rd party control will be ‘unintelligent’. See more here
The Greenstar Sense made by Worcester gives weather compensation or load compensation options. On the front of most of their range is a control panel with push buttons. This has smart connectivity built-in so you can connect to Worcester’s own EasyControl system. This provides another option of load compensation and allows the user to control their heating and hot water through an app which we find very good.
Although Worcester boilers can run either weather compensation or load compensation control systems they are nowhere near as advanced as Viessmann and the control screen on the front of their higher-end boilers does not display as much information as the Viessmann do.
Worcester was originally founded in 1962 and really pushed forward oil and gas boiler innovation and became part of the Bosch group in 1996. Their UK headquarters are based in Worcester. Their product range includes gas and oil boilers, hot water cylinders, renewable technologies like heat pumps and solar thermal systems. As well as controls and accessories. Their gas boilers are manufactured at their main headquarters and their oil boilers are produced at another site in Clay Cross, Derbyshire.
Worcester is a UK innovator, a lot of their innovation is still complete here and should be seen as a credit to the UK, although owned by Bosch. They are a more well-known brand than Viessmann largely because they seem to have a lot more of their budget for advertising. It is also worth mentioning over the years Worcester has built a good reputation for customer service, in fact, we would argue one of, if not the best, which should and does stand well in their stead!
Viessmann was founded in 1917 and has been family-owned since its arrival on the scene. Their headquarters are housed in Allendorf in Germany. Allendorf is a municipality situated in northwest Hesse, Germany. The municipality is within the Waldeck-Frankenberg district in the rural region called the upper Eder valley. Allendorf is internationally known because of Viessmann.
Today Viessmann manufactures heating, industrial and refrigeration systems and operates in over 70 countries throughout the world.
They have operated within the UK since 1989 from the UK headquarters in Telford. Their product range includes gas and oil boilers, air and ground source heat pumps, biomass and steam boilers and combined heat and power generation units.
Although Viessmann are not as well known as Worcester Bosch is in the Uk, they are increasingly becoming a more recognised brand.
Viessmann are innovators to the industry. They are constantly introducing new products, methods and ideas and spend roughly 5 million euros a week on research and development. This drastically exceeds any other competitor in the market.
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