🫁 Pneumonia, not gastroenteritis
Legionnaires' Disease is not a simple cold. It is severe pneumonia with high fever (above 39 °C), headache, muscle pain and shortness of breath. Mortality reaches 10-15% even with treatment.
Legionnaires' Disease (Legionella) Prevention: The Invisible Danger in Your Hot Water
Legionella pneumophila is a bacterium naturally present in water. Normally harmless - but if it finds the right temperatures, it multiplies uncontrollably and causes Legionnaires' Disease, an extremely severe and potentially fatal form of pneumonia.
What this bacterium is, how it spreads inside your own bathroom, and how a simple button press (the Thermal Disinfection Cycle) eliminates the risk.
1. How Do You Catch It? The "Drinking Water" Myth
There is a huge misconception. You do not catch Legionella by drinking contaminated water - your stomach would destroy the bacterium. The danger lies in the lungs.
Infection occurs through inhaling microscopic water droplets (aerosol) suspended in the air. The most common risk points at home: when you shower and breathe in the steam, in jacuzzis (hot tubs) that produce bubbles, and in dirty humidifiers.
🏨 Who is at risk
The elderly, smokers, immunocompromised individuals. Hotels, hospitals and care homes are particularly at risk due to large hot-water networks with many stagnation points.
🚿 Shower risk
Every time you turn on the shower, a cloud of aerosol is created. If the water contains Legionella, you inhale it deep into your lungs without even realising it.
🫧 Hot tubs & humidifiers
Jacuzzis (hot tubs) produce bubbles - a perfect dispersal medium for bacteria. Dirty humidifiers that are not cleaned regularly are also a source of risk.
2. The Heat Pump "Paradox": The Dangerous 25-45 °C Zone
Why does this bacterium concern modern homes so much? Because it loves the temperatures at which heat pumps operate!
❄️ Below 20 °C
The bacterium is in hibernation. It does not multiply, but it does not die either - it waits patiently for the temperature to rise.
⚠️ 25-45 °C: The Party Zone
Here Legionella reproduces exponentially. A heat pump cylinder set to 45 °C for economy is the perfect incubator, especially if the water remains stagnant for days.
🟡 50 °C: Growth stops
At 50 °C the bacterium survives, but stops reproducing or reproduces minimally. This temperature is not enough for complete elimination.
🔴 60 °C+: Death
At 60 °C and above, Legionella dies. This is the target of the thermal disinfection cycle - a weekly "heat shock" that sterilises the entire cylinder.
3. The Solution: The Thermal Disinfection Cycle (Anti-Legionella)
Since we want the economy of 45 °C, how do we kill the bacterium? The answer is "Thermal Shock". All modern heat pumps and smart boiler thermostats have the Anti-Legionella function built in.
⏰ How it works
The system is programmed to perform a hot-water "attack" once a week - typically at dawn on Sunday (e.g. 03:00), when nobody is showering, to avoid any scalding risk.
🌡️ 60-65 °C for 30-60 minutes
The heat pump fires its immersion heater and raises the cylinder temperature to 60-65 °C , holding it there for 30-60 minutes. Afterwards, it returns to the economical 45 °C.
📋 Commissioning: MUST be activated
The installer MUST activate this function during commissioning. If it wasn't done, check the DHW (Domestic Hot Water) menu → Anti-Legionella → ON.
💰 Cycle cost
The immersion heater (2-3 kW) runs for 30-60 minutes: €0.30-0.50 per cycle - roughly €2 per month. A negligible cost compared to the risk.
4. Solar Water Heaters, Holidays & Stagnant Water
Solar water heaters boil the water in summer (80-90 °C), so there is no problem. The risk comes in winter : after days of overcast skies the water stays lukewarm (30-40 °C) - ideal for Legionella.
☀️ Solar in winter
If you haven't seen sun for days, switch on the immersion heater (the panel switch) for 1 hour. The water will reach 60 °C+, fully sterilising the cylinder.
🏖️ Holiday rule
Legionella loves stagnant water. When you return from holidays (15+ days), BEFORE showering: remove the shower head, place it on the bath floor, turn to "full hot" and let the water run for 2-3 minutes.
🔑 Why on the floor?
You place the shower head low so it does not spray aerosol into your face. You want the pipes to flush without you inhaling potentially contaminated droplets first.
📊 Final summary
Don't sacrifice your health for half a euro of electricity per week. Weekly thermal disinfection (60 °C+, 30-60 minutes) - activate it on the heat pump, fire the immersion in winter, flush after holidays.
⚠️ Make sure the Anti-Legionella cycle is ON on your heat pump. It costs ~€2/month. Safety is non-negotiable!
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