Both Worcester Bosch and Viessmann offer quality engineering across their boiler ranges. However, when pitched against each other, Viessmann stands out as the better boiler for us.
Quality of components
For us, Viessmann winning is largely due to the quality of their components. Unlike Worcester Bosch, Viessmann does not use plastic components in any of its boilers. Nor do they utilise an aluminium heat exchanger like Worcester Bosch. It is the quality of their internal components which really sets Viessmann apart.
Stainless steel heat exchanger
A patented product, the Stainless Steel Inox-Radial Heat Exchanger is highly resistant to corrosion in a wide range of pH levels. Whereas for aluminium, if the proper fluids are not used to produce and maintain a narrow pH range, it will corrode much faster. Without the use of proper fluids, you may damage an aluminium heat exchanger. If you do damage the heat exchanger, your warranty will be voided, because the manufacturer will cite improper use of fluids.
In direct comparison, stainless steel heat exchangers do not require special fluids, are compatible with plain clean water and commonly available propylene glycol.
Whilst aluminium is lightweight and has better thermal conductivity initially, stainless steel will be of much better value for money due to its longevity and better resistance to corrosion. Aluminium will rust, corrode, warp, and break down long before stainless steel, so investing in a boiler with a quality stainless steel heat exchanger will increase the useful life of your boiler.
Granted, stainless steel is more expensive to source and manufacture but it is a long-term investment. An investment Viessmann made by manufacturing it in-house at their facility in Germany for quality control.
Built-In Shock Arrestor
The built-in shock arrestor used in Viessmann’s boilers is another plus point for the range and will reduce any water hammer issues experienced.
If you are unaware of what water hammer issues are, they are the loud rattling of pipes every time a tap is opened. A water hammer is a pressure surge or wave caused when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change). A water hammer commonly occurs when a valve closes suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe.
PRV and Condensate Combined
Throughout the Viessmann boiler range, the pressure relief pipe and condensate are combined. This gives the installers more choice in siting the boiler, allowing a lot more flexibility with replacement, retrofitting, and new boiler installations.