Protherm Lev 25 KKZ 90 with connection set

• Higher solar gain
• Also suitable for environments with high outdoor temperatures - smooth start-up
• Longer service life due to lower thermal stress

• Access to all components and connection points from the front of the boiler
< li> Easy access to electrical connections
• Easy connection of the boiler to the heating system
• Possibility to divide the boiler into two parts for easier handling

Frequently Asked Questions

• How exactly do I choose the output of a PROTHERM condensing boiler? The starting point is the calculated heat loss of the heated building (most reliably 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. An oversized boiler cycles on and off more often, which shortens its lifespan and reduces efficiency; an undersized boiler cannot adequately heat the house on very cold days.
• Why is a condensing boiler more economical than a conventional one? A condensing boiler also makes use of the heat hidden in the water vapour produced during gas combustion - in a conventional boiler this leaves unused through the flue, whereas 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. This allows condensing boilers to reach efficiency of around 105-110% relative to the calorific value of the gas, compared with the usual 85-92% for conventional boilers.
• What type of flue does this boiler need? Most modern condensing boilers are so-called “turbo” units (with a sealed combustion chamber) and require a concentric or separate flue and combustion-air intake routed through the perimeter wall or roof - so a functioning chimney is not needed. You will find the exact type and maximum length of the flue (for a diameter of 60/100 or 80/125 mm) in the technical documentation for the specific model, or you can consult our customer service.
• What does the ErP energy class shown for the boiler mean? This is the mandatory efficiency labelling for heating appliances under the EU ErP (Ecodesign) Directive, similar to the energy labels used for refrigerators. Condensing boilers commonly achieve class A, or even higher in combination with room control (e.g. A+ when using equithermal control and a room thermostat).
• What is a cascade connection of boilers? This means linking several boilers into a single system so that together they can cover a higher output than a single boiler could achieve - suitable for larger buildings (apartment blocks, commercial premises). The system switches on further boilers gradually according to current demand, achieving high efficiency even with fluctuating heat demand.
• Can I install and connect this boiler myself? No. Connection to the natural gas supply, the electrical network and the flue is, by law, reserved exclusively for a person with the relevant authorisation (most often an authorised service technician for the given brand or a gas equipment inspector). 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 to maintain the warranty even after its standard expiry (an extended warranty subject to regular servicing is common especially for Vaillant, Protherm and Viessmann). You will find the exact warranty conditions in the warranty card 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 tank, room control and other accessories in the case of a set) are stated in the product name and in its technical parameters above on this page.