BOSCH BASIC 15 2300 + WST 120-5 O + CR 120

Frequently Asked Questions

• How exactly do I choose the right output for a BOSCH condensing boiler? The starting point is the calculated heat loss of the building being heated (most reliably taken from the project documentation or an energy certificate). If you don't have a project, you can estimate roughly 60-100 W per m² of floor area for a normally insulated house built after 2000, or 100-150 W/m² for an older, uninsulated house - the exact figure varies depending on the number of floors, ceiling height, number and quality of windows, and building orientation. A boiler oversized for its output switches on and off more frequently (so-called cycling), which shortens its lifespan and reduces efficiency; an undersized boiler, on the other hand, cannot heat the house sufficiently on freezing days.
• Why is a condensing boiler more economical than a conventional one? A condensing boiler additionally uses the heat hidden in the water vapour produced when burning gas - in a conventional boiler this leaves unused through the flue, while in a condensing boiler it is cooled below the so-called dew point, the vapour condenses, and the released heat is returned to the heating circuit. Thanks to this, condensing boilers achieve an efficiency of approximately 105-110% relative to the calorific value of the gas, compared to the usual 85-92% for conventional boilers.
• What type of flue gas discharge does this boiler need? Most modern condensing boilers are so-called turbo boilers (with a sealed combustion chamber) and require a coaxial (concentric) or separate flue gas discharge and combustion air supply routed through an external wall or roof - so they don't need a functional chimney. You can find the exact type and maximum length of the discharge (for a diameter of 60/100 or 80/125 mm) in the technical documentation for the specific model, or consult our customer service.
• What does the ErP energy class stated for the boiler mean? This is a mandatory efficiency label for heating appliances under the EU ErP (Ecodesign) directive, similar to the energy labels on refrigerators. Condensing boilers commonly achieve class A, or even higher in combination with room controls (e.g. A+ when using weather-compensated control and a room thermostat).
• Can I install and connect this boiler myself? No. Connection to the natural gas supply, the electrical network, and the flue gas discharge is, by law, reserved exclusively for a person with the relevant authorisation (most often an authorised service technician of the given brand or a gas equipment inspection technician). After installation, the boiler must be commissioned by the manufacturer's authorised service, which is usually also a condition for the warranty to be valid.
• What about servicing and the warranty? Most manufacturers require a regular annual service inspection by an authorised service provider in order for the warranty to remain valid even after its standard expiry (an extended warranty for regular servicing is common especially for the brands Vaillant, Protherm, and Viessmann). You can find the exact warranty conditions in the warranty certificate supplied with the boiler.
• What is included in the delivery of this specific product? The exact contents of the package (the boiler itself, possibly a hot water storage cylinder, room controls, and other accessories in the case of a set) are stated in the product name and in its technical parameters above on this page.