Question about DHW temp and Legionnaires

[BobbyJoe]

Question about DHW temp and Legionnaires.

1 year old Combi boiler, hot and cold water is delivered throughout the flat via the main water feed
I have no water tanks or cylinder in flat just a combi boiler

Does it matter what temperature I set the DHW to? Is there a legal temperature that the hot water in your home should be set on for example my boilers DHW lowest temp is 35 degrees and the highest is 60 degrees and their is also a hot water survivor function which delivers water at 55 degrees Celsius.

I mention legionnaires as how does it occur and is there any chance of it with a combi boiler?

Any information would be appreciated many thanks

 

[oz-plumber]

Legionnaires is not a problem with combi boilers, because the temperature of the water fluctuates too much for the legionella to breed.

Generally happens in storage cylinders where the constant temperature is between 35 C + 50 C.
Stored water should be kept at a minimum of 60C to kill off the bacteria

 

[BobbyJoe]

Great that is good to know thank you

 

[Dr John Doolittle]

Am I going to be the only one who asks how this particular bacteria is introduced into your home in the first place?

 

[snowhead]

Am I going to be the only one who asks how this particular bacteria is introduced into your home in the first place?

It comes into the home, or building, in the water supply.

 

[Dr John Doolittle]

It comes into the home, or building, in the water supply.

So its everywhere? like covid19 virus?

 

[snowhead]

It's a bacteria, is probably more widespread than Covid and been around far longer, but is harmless untill there's a suitable environment for it to multiply, water @ 20c to 50c is perfect.
It then needs to be atomised small enough to enter the lungs.

 

[Dr John Doolittle]

It's a bacteria, is probably more widespread than Covid and been around far longer, but is harmless untill there's a suitable environment for it to multiply, water @ 20c to 50c is perfect.
It then needs to be atomised small enough to enter the lungs.

So water treatment does not remove kill it! So if it's this dangerous, why don't we have to boil all water coming into the home?

 

[snowhead]

Drinking Legionella won't harm us.
Incidents in the U.K are relatively rare.
Cases originating from Domestic systems in the U.K range from almost unheard of to zero.
Although like everything else that may change in the future.

The source is either found to have come from Commercial buildings / Heathcare situations or it's never traced.

 

[Dr John Doolittle]

so the question raised could then be described as pointless and irrelevant in a domestic situation ?

 

[oz-plumber]

Not irrelevant.

The systems installed have been designed not to allow the bacteria to bloom.
The perfect temperature is 38C.
Hot water cylinders are set to 60 C to kill off the bacteria.
The bacteria remains dormant in temperatures less than 20C
Combi boilers have too much temperature variance over shorter periods of time for the bacteria to cause problems.

 

[Ric2013]

so the question raised could then be described as pointless and irrelevant in a domestic situation ?

Not irrelevant. There are laws about stored water temperature that apply to domestic.

In terms of practicality, as hot water does form vapour, it is possible to catch Legionnaries' Disease by inhaling the vapour, particularly from a shower.

The disease does need to get into the lungs, however. The issue is that the bacteria are in the mains water in low quantity and not enough to cause you to catch anything, even if, I suppose, you were to choke while drinking the water and it got into your lungs.

If the cold water is heated and stored at the right temperature, say 40°, the bacteria can breed and then the water could be dangerous. Above 55°, the bacteria stop breeding and start to be killed off slowly.

At 60°, they die off quite fast which is why 60 is the legal minimum for stored hot water.