Short & direct
Legionella multiply in lukewarm water between about 25 and 45 °C and die off above around 60 °C. Set the boiler to at least 60 °C so that roughly 55 °C still reaches the taps. This keeps hot water hygienically safe – temperatures kept too low purely to save energy are risky.
Setting the boiler too low to save money risks a health problem: legionella. With the right hot-water temperature you keep the water hygienically safe – without wasting energy unnecessarily.
What is legionella – and why is it dangerous?
Legionella are bacteria that occur naturally in small amounts in water. They become dangerous when they multiply strongly in lukewarm water and are inhaled via fine droplets – for example while showering. An infection can lead to Legionnaires’ disease, a severe form of pneumonia.
The right boiler temperature
The temperature in the hot-water system is decisive:
- Danger zone: about 25 – 45 °C – where legionella multiply most.
- Safe: from around 60 °C the bacteria die off.
Set the boiler to at least 60 °C so that about 55 °C still reaches the taps. This keeps the system hygienically sound.
Important: Don’t permanently lower the temperature below 60 °C just to save energy. The risk is out of all proportion to the small saving.
Save energy without the risk
You can still save – but the right way:
- Insulate the boiler and pipes well.
- Set the circulation and timer sensibly instead of lowering the temperature.
- Flush rarely used lines regularly so no water stagnates.
Boiler care against limescale and germs
A scaled-up boiler heats inefficiently and offers deposits where germs can persist. Our article on descaling a boiler shows how to keep it in shape. We handle the annual check as part of our maintenance service.
Call us on +41 44 747 06 61 or request your free quote.
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