Central mixing valve near unvented cylinder

[AndyCoo]

Hi all
I have a mixing valve question.
Should I have one fitted close to my new unvented cylinder?

 

[ShaunCorbs]

Ideally no why do you ask ?

 

[AndyCoo]

Sorry the spam filter is making it impossible to post more details on my reasoning behind this idea.

 

[AndyCoo]

Ideally no why do you ask ?

If the hot is mixed centrally I was thinking that this is more efficient than 15m of v hot water travelling to the basin, being mixed there and then cooling down again in the long pipe run.

 

[AndyCoo]

If the hot is mixed centrally I was thinking that this is more efficient than 15m of v hot water travelling to the basin, being mixed there and then cooling down again in the long pipe run.

Instead, why not send pre mixed water everywhere at 40deg?

 

[ShaunCorbs]

Legionella would be a problem

 

[AndyCoo]

Thanks Shaun.
Could you explain why this is an issue?
If my cylinder water is still at 60degC, is there a risk of Legionella just in the hot pipework between mixing valve and taps?
I expected this would be no different risk than the case of a combi boiler putting out 40deg C water that then cools in the equivalent pipework.
Sorry for persisting, just trying to understand properly why it’s not generally done.
Thanks again for your advice.
Andy

 

[Gasmk1]

What about kitchen tap water won’t be hot enough for washing stuff, combis are low risk

 

[AndyCoo]

Good point, thanks.
I was thinking that hand-safe water temp is the same for kitchen sinks and wash basins. But maybe they’re different as only adult hands use the kitchen sink.
Is that the logic?
I understand that combis are generally low risk. I suppose I thought that as long as the cylinder is at 60, the legionella risk is eliminated so it doesn’t matter what temp the water in your pipes is.
Happy to learn that this is not the case though.
Thanks very much for the discussion.

 

[AndyCoo]

Found this good HSE link that says:
Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified)

Looks like case closed.
Thanks for your inputs everyone.
Andy