Lowering water boiler temperature - health hazards?

GingerTim

It can take as few as two days for legionella to grow where the boiler is kept at between 20 and 45 degrees - given the right conditions.

Vincero

wild666 said:

I'm running my hot water at 50 degrees all the time. I use the kettle to boil water for drinks and washing up and put about 4 titres of cold water into 1.7 litres of boiling water it hasn't had any effect on me since I lowered the temperatures in September 2021.

That's less of an issue with fresh water as the bacteria needs some time to develop, and also it contains low levels of chlorine which prevent growth. Over time that fades, so heated water which relies on a storage tank (don't forget apart from the water sitting in the hot water cylinder, it may have been sitting in a loft header tank for a while before) is more risky.

Rodders53

The HW cylinder described is almost certainly a vented "combination cylinder" type... where the cold water tank is over the stored hot water vessel... thus the stored cold will warm up over time to potentially above the 20-25C level  where legionella bacteria are dormant.  IF there's legionella bacteria in the incoming water supply (and not all killed by the water treatment chemicals) that is.

So with this tank arrangement I'd suggest it's pretty much essential that the water is raised to 60C and stored like that?  60C is 140F.

ProDave

Just for a bit of extra info.  You really only need to heat your hot water to 65 degrees when you have a vented water cylinder like the OP (fed from a header tank)

If you have an unvented, pressurised water tank that is fed with treated mains water, then there really is no need, as there will be no bugs in the water coming in, and no means for any contamination to enter.  I heat out unvented water tank to 48 degrees and have been doing so for several years.

Section62

Vincero said:

Section62 said:

TMV's - if used - should be located as close as possible to the point of use, not the source of heat or storage.

It's possible I've seen a bodge where it's been used before near cylinder to avoid using multiple of them and also to avoid needing additional check valves by using the hot water feed and the cool water from the header tank...
As always, one should consult a reputable plumber or if doing the work themselves RTFM.

As you say, a bodge.  Possibly by someone not understanding the risks associated with legionella.

It doesn't make sense to install a TMV for the purposes of allowing the heat source to be run hotter to kill legionella if you then have long runs of distribution pipework containing water at risky temperature levels due to lowering the temperature with a TMV.

The basic principle is to try to keep hot water 'hot' and cold water 'cold'.  The hotter the hot water for as long as possible, the less opportunity for legionella to thrive.

Ectophile

EcoScruples said:

I'm sorry but that's actually some really bad advice.
There's an approved code of practice by the HSE that advises you heat hot water storage tanks to 60 degrees for a min of 1 hour on a daily basis to eliminate the risk to legionella growth.
If you're running your tank at 45 degrees for a week then you're promoting the perfect conditions for bacterial growth.

But if we're all going to switch over to heat pumps for our heating, then that's not going to happen.

Heat pumps are good at producing warm water, but the efficiency drops off rapidly as you set the temperature higher.  So it's possible to heat a tank to 45C off a heat pump, but 60C means turning on the immersion heater.

If you have to use the immersion heater every day to heat up the water, then you've lost most of the efficiency benefit of having a heat pump.  That's why the timer is normally set to once a week.

Vincero

Ectophile said:

If you have to use the immersion heater every day to heat up the water, then you've lost most of the efficiency benefit of having a heat pump.  That's why the timer is normally set to once a week.

Not really, if you're comparing the use of either against a gas boiler - immersion heaters are efficient, but are more costly than gas.

But I agree with the sentiment - the 'benefits' in terms of potentially lower bills will be nullified. Ideally the use of solar to heat the water (or to power immersion heating) could reduce some of that energy usage but these are not exactly cheap to buy or fit.

EcoScruples

No problem, I can only advise on the safest way but by the sounds of it many people run their water in many different ways.
I myself have a 120 litre hot water cylinder (fed from a 270 litre storage tank in the roof) that I heat once a day for 1 hour using my solar/battery.
It doesn't always take 1 hour, if I didn't use much hot water the previous day then it can take 35 mins.
I'm safe in the knowledge though that my water is legionella free.

Mstty

Well yes if you have a separate water storage tank in the roof rather than an unvented sealed system that is safe approach.

Makes sense why you are cautious.

Ally_E.

I often scald my hands washing dishes when temperature is 50C+, our kitchen tap doesn't mix hot and cold very well. That's another reason I like to keep the temperature at around 45C and do a boost once a week to higher temperature. Need to replace that tap really, as that's a poor excuse.