Lowest temp to kill legionella?

waqasahmed

So I was experimenting with my boiler last night  and I got it down to 45C for the radiators, and that worked fine. I'll try putting it to 42C and see if that works too, and then 40C (lowest)

Any way, I was wondering what's the lowest temperature needed to kill legionella? I've seen 60C quoted which is the highest temperature for water, on your boiler but equally I've seen sources mention that 50C is good to kill off legionella too

Spies

You don't need to worry about legionella in the radiators as it's not drinking water

You should have seperate controls for your CH and DHW

Boffinboy24

Dependent on the system, that’s not the case. I have a modern system boiler that unfortunately only has one temperature setting. Whilst I can separately turn on heating circuits or hot water cylinder from the stat the temperature of water used is the same as it’s just interpreted as a call for heat.

I need to figure out how easy / expensive it is to add a separate hot water channel / temperature because it means I need to keep the temp above 60. Particularly frustrating as I have underfloor heating on the ground floor, which mixes the 60 degree water with cold to get to a lower temp. I have radiators upstairs. 

I know the model of boiler does come in a version with separate controls for the temperature, but am not sure if it can be retrofitted. 

Reed_Richards

You should usually be able to set a different temperature for your central heating and your hot water cylinder.  I read that Legionella is killed by 2 minutes at 60 C or 2 hours at 50 C.  But when your hot water cylinder is at any set temperature in fact it will tend to be hotter at the top and colder at the bottom.  One hour a week at 60 C is generally held to be sufficient. 

Boffinboy24

If the OP has a system boiler setup  like mine, again that may not be possible. In my case the cylinder also has an adjustable stat, I assume it controls whether the valve to the coil is open for hot water, though I’ve not fully investigated. The stat on the cylinder doesn’t control the flow temperature from the boiler - if I set the boiler at 50 degrees flow temp for efficiency then the cylinder will never reach 60 I assume as the water heating it is not hot enough. If the OP has the same kind of system boiler setup they may get the same problem! In terms of temperature an hour at 60 is usually recommended, for example Vaillaint recommend 60 to be confident it’s safe and talk about below 50 as potentially posing a risk: https://www.vaillant.co.uk/homeowners/advice-and-knowledge/hot-water-tank-temperature-2416051.html

Screwdriva

We set our DHW at 52 degrees with a once weekly legionella cycle at 65 degrees 

HampshireH

Spies said:

You don't need to worry about legionella in the radiators as it's not drinking water

You should have seperate controls for your CH and DHW

If you follow this and have a lower setting just on your rads don't bleed them or have any maintenance carried out. Lower temperatures are a prime breeding ground for bacteria 

Your system needs to be heated and flushed though regularly  to maintain it or the next time you bleed your rads or need to work on one you could be releasing bacteria in water droplets.

Might not be drinking water but you don't want to be the cause of you/your plumber getting sick

Reed_Richards

If I bleed a radiator I always use a bit of paper towel to catch any water that comes out, no droplets.  And the water in radiators usually has additives which I doubt make it a comfortable breeding ground for bacteria.  

waqasahmed

Spies said:

You don't need to worry about legionella in the radiators as it's not drinking water

You should have seperate controls for your CH and DHW

I was more getting at hot water? It's a combi boiler and water is heated by gas too 

Reed_Richards

A combi boiler will have no problem with Legionella because hot or warm tap water is not stored.  You should also be able to set the hot water temperature completely independently of the radiator water temperature.

waqasahmed

Reed_Richards said:

A combi boiler will have no problem with Legionella because hot or warm tap water is not stored.  You should also be able to set the hot water temperature completely independently of the radiator water temperature.

Awesome. In that sense, I could theoretically try and see if I could get it down to say 40c and see if it still comes out at a reasonable temperature?

I have this

https://www.mrcentralheating.co.uk/vokera-easi-heat-plus-29ci-erp-combi-boiler-flue-easy-pick-pack