short heating element in cylinder- risk of legionaires disease?

[shackec]

I have recently installed an immersion heater with dual heating elements; controlled by a sink/bath switch. It is likely that only the short heating element will be in use over a fairly long period of time (six months?). The bottom three quarters of the tank never heats up. The cold water inflow is 4" from the bottom of the tank.
I am assuming that the regular inflow of cold water to replace used hot water would be sufficient to avoid the possibility of stagnant water and legionaires disease.
Does anyone have a view on this? Grateful for any comments.

 

[CBW]

I doubt legionnaires would occur, as the top half is heated (as long as it’s enough to kill bacteria - 60 - 65 degrees range) and the water is always replenished

 

[JohnD]

What colour is the cylinder?

 

[ChrisJP]

Maybe it's my ignorance, but what has the colour of the cylinder got to do with whether its heating enough to stop legionaires disease?

 

[shackec]

Thank you all. The cylinder is a stainless steel cylinder and is covered with insulation. I know that some bacteria thrive, or otherwise, in the presence of some metals. Whether that is true of copper vis-a-vis stainless steel I do not know.
The thermostat is factory preset at 60 degrees. I am inclined to increase this to, say, 70 degrees?

 

[foxhole]

Legionaries requires air and stagnant water , it’s been found in header tanks and even shower heads, but the hot water tank gets replenished in daily use .

 

[shackec]

I have recently installed a dual element immersion heater. I am having difficulty in getting the bath element to heat the entire tank. A subject for a different post I think. However, this did make me think about the risk of legionaires disease. I think I might have over-reacted to some marketing ploys! Thanks again for responses. regards. Charles

 

[JohnD]

Maybe it's my ignorance, but what has the colour of the cylinder got to do with whether its heating enough to stop legionaires disease?

Most householders can recognise the colour even if they cannot define their plumbing system, so it's an easy question to answer.

OP has not said what colour it is, but the colour usually tells us approximate age and if it is vented or unvented.

An unvented cylinder is fed directly from the cold incoming waterman and unlikely to be contaminated. A cylinder fed with a cold supply will stratify. The hot and cold do not mix to form warm water. The hot water at the top is effectively pasteurised, and being stored, hot, will destroy most microorganisms. The cold water at the bottom is probably uncontaminated, and is also too cold for legionella to thrive and grow, and is replenished with more cold water each time a tap is run.

A vented cylinder, fed from a water tank in the loft, may receive water that is contaminated and/or has been standing for days in a loft heated by the sun and ideal for bacterial and fungal growth. Older systems are more often dirty which provides nutrients for microorganisms.

BTW copper does have some antimicrobial effect, though not total. Stainless can get biofilm, so I guess is not so good in that regard. Neither can be relied upon, so if necessary can be sterilised with heat or chemicals.

Water stored at 60C will kill legionella. The hotter it is the faster it dies. IIRC it dies slowly at 50C, which is OK if you keep the cyIinder hot.

Edit: "The bacteria multiply where temperatures are between 20-45°C and nutrients are available. The bacteria are dormant below 20°C and do not survive above 60°C." https://www.hse.gov.uk/healthservices/legionella.htm

Hope this helps.