Optimum boiler temp and hot water temp

I have a Vaillant EcoMax Pro condensing boiler and also a Superduty fast recovery hot water cylinder. When the boiler was installed the installer set the boiler temp to 65C. A year later, a different guy from the same firm came round to do the 1 year warranty check and insisted it should be 70C. What is the optimum value, if there is such a thing? Or would I be right in thinking that it's the return temp that's more important, and that it should be 55C or less?

If it's the return temp that's important, then I have a supplementary question... I understand that hot water in a cylinder should be heated to

60C in order to prevent the growth of Legionella bacteria. Is this correct, and if so, how do I reconcile the two requirements -- return at 55C or less, but hot water >= 60C?

Ta,

Steve S

Reply to
Steve S (another one)
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The 60C is only for the first use, to 'kill' any harmful bacilli in the equipment.

Mary

Reply to
Mary Fisher

"Mary Fisher" wrote :>

Hmm. Could the tank in the loft not be a potential further source of contamination? It's not accessible to anything larger than an insect, but... I'm just trying to anticipate my wife's arguments here, and she's somewhat paranoid about germs.

Reply to
Steve S (another one)

On Fri, 14 Mar 2008 11:58:07 GMT someone who may be "Steve S \(another one\)" wrote this:-

It shouldn't be accessible to an insect, as insect screens should be fitted to it.

Germs have always existed and always will. Your wife breathes them in all the time.

Reply to
David Hansen

Does she breathe?

Reply to
Mary Fisher

Oh, sorry David, I sent a reply before reading yours.

Mary

Reply to
Mary Fisher

That's the least of her worries, but it's nice to see the technical ignorami (Dynamo Hansen and the She-Devil) focusing on the wrong thing.

Reply to
Steve Firth

On Fri, 14 Mar 2008 15:31:03 +0000 someone who may be %steve%@malloc.co.uk (Steve Firth) wrote this:-

Nice try. However, those of us who were once responsible for water quality monitoring in a variety of systems, including olympic sized swimming pools and numerous air conditioning systems, know just how to evaluate such assertions.

Should you wish to make some more wide of the mark assertions you may have the last word.

Reply to
David Hansen

That's the real problem.

They are focusing on the right thing, a person "somewhat paranoid about germs". We have very effective immune systems that'll deal with billions of bacteria a day.

Assuming this is a modern installation and the roof tank is fitted with a full By Law 30 kit. Contamination of the water in that tank is a minimal risk. It's mains fed with chlorinated water it is highly unlikely anything will grow in or get into the tank.

Reply to
Dave Liquorice

I'm not into plumbing but this is the temperature to aim for to keep the boiler in condensing mode, if you haven't a large enough load on the system then the return temperature will be higher, the boiler won't be in condensing mode and eventually it should switch off.

I'm not sure of the recommended temperature to kill Legionella bacteria but they fester in warm re circulating or stagnant systems, so if the water in the cylinder gets heated to above the recommended temperature the bugs get killed.

If cold water tank is less than 50C and DHW tank above the coil is heated to greater than 60C I cannot see how the bugs would survive.

AJH

Reply to
AJH

I wonder why you have to boil stuff for several minutes to kill bacteria if an initial burst of heat will do the job?

Reply to
dennis

You were a pool boy and a janitor? That figures.

Reply to
Steve Firth

It's quite interesting, then, that some solar heating companies and many public bodies say that the hot water should be heated to at least 60C at least once per week, if a shower is to be fed. However, it would appear that any temperature above 50 will kill them (Legionella bacteria, not the public bodies!), if slowly, according to some sources. They apparently survive quite well in cold water, by the way.

Reply to
Steve S (another one)

The worry in water heting equipment is about specific bacilli.

What bacilli do you kill at several minutes of boiling? And how does any central heating/domestic hot water system maintain boiling for several minutes?

Mary

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Reply to
Mary Fisher

...

er - they have to be there at the start ...

Reply to
Mary Fisher

This is my take on the settings.

If the boiler knows the difference between doing the HW and CH then the best settings (IMHO) is HW max and CH as low as possible but still capable of heating the house. I think the Vaillant does know the difference if it is wired up correctly, but that may including using proprietary controls.

If the boiler does not know the difference between HW and CH (almost all) then I suggest setting the flow at about 10C more than the thermostat on the HW cylinder, if that's not enough to heat the house then consider adding more radiators. Typcically HW temps are sett to 55-60C so the primary flow temp should be 65-70C.

HTH

Reply to
Ed Sirett

The correct answer is not many, it takes longer for most. However you kill a lot of each type.

Reply to
dennis

Thanks Ed. Just what I was looking for.

Reply to
Steve S (another one)

...but only if you keep exposing the immune system to germs. It stops working if you stop exposing it to germs, and that includes Legionella.

Reply to
Andrew Gabriel

Leaving the most powerful (therefore 'dangerous') to survive then!

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Reply to
Mary Fisher

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