Legionella bacteria pose a significant risk in domestic hot water systems. That is why Master Therm heat pumps include a dedicated Antilegionella function, which heats the storage tank to a safe temperature and eliminates these microorganisms.
Where Does Legionella Most Commonly Occur?
Legionella is a naturally occurring bacterium found in aquatic environments, especially in fresh surface water, but it can also occur in soil. In most situations, it does not pose a threat to humans — it becomes dangerous when it enters artificial water systems and finds ideal conditions for growth.
Most common sources of Legionella:
Domestic hot water at 20–50 °C
Showers, heat exchangers, cooling towers
Clogged shower heads, water distribution systems, storage tanks
Stagnant sections of piping where water does not circulate
Risk Factors for Legionella Growth
Water temperature 20–45 °C – ideal range for rapid multiplication, with a peak at 35–43 °C
Stagnant water – long-unused showers
Biofilm and sediment – deposits on pipes, seals, shower heads
Insufficient disinfection – missing chemical or thermal maintenance
Poor system design – dead legs and low-flow areas
Antilegionella Program in Master Therm Heat Pumps
The automatic weekly overheating of the domestic hot water tank to a safe temperature ensures water free of Legionella. The user can set the temperature in the Domestic Hot Water menu. The process repeats once a week to guarantee hygienically safe hot water.
Our new highly efficient R290 heat pump series (air-to-water, ground-to-water) can heat water up to 75 °C using only the compressor, without the need to activate an electric boiler, contributing to overall energy savings.
Heat pumps using R407c and R410a refrigerants (air-to-water, ground-to-water) use a combination of compressor operation and a bivalent source. The compressor raises the tank temperature as high as possible until the safety sensors stop it. The bivalent source (built-in electric boiler) then heats the water to the final temperature required to eliminate Legionella.
Regular high-temperature heating is one of the most effective preventive measures, as Legionella cannot survive at elevated temperatures.
Why Is Prevention Important?
When showering, fine aerosols are formed—and they may contain Legionella. If inhaled into the lungs, they can cause Legionnaires’ disease, a serious type of pneumonia. For this reason, proper maintenance of domestic hot water systems, shower heads, and piping is essential — and the Antilegionella function is one of the key protective features.
