Our Nest thermostat has a built in anti bacteria setting. If in any 48 hour period the hot water hasn't been heated for at least two consecutive hours, it turns on the boiler and runs it for ages.
I've turned it off, because with our schedule it's on at every opportunity. I also run the water at much lower than 60 degrees, because that's much too hot from the tap.
A quick poke about the webs reveals "safety sites" that say Legionella is a big thing, and I'm mad.
A bit deeper, and it looks like UK legionella is pretty rare, especially from domestic systems.
So before I decide to leave this expensive Nest option off permanently, what do you do, and do you run at 60 degrees?
Last edited by: Crankcase on Wed 2 Aug 23 at 08:41
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I set mine lower, at about 55 IIRC, as an economy measure last winter and I'm still here to talk about it.
You've got solar panels haven't you? I bought a thing which diverts unused solar to my immersion and most spring/summer weeks my gas usage is below 50p (unfortunately not the standing charge though). (Actually that device feels like it nearly boils the water on a good solar day, but only the top bit of the tank - though I did have one of those longer immersions fitted)
I'd also consider changing my gas supplier to the Octopus Tracker tariff to make it cheaper - 3.8p today. :-)
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Run mine at 60c on the button. Might consider shaving 5c off that if prices rocket again.
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Can't remember the actual number now without looking stuff out but when I did a City and Guilds Energy Adviser accreditation for work we were told that HW should be kept higher than you'd think for Legionella.
Turned home down from 60 to 55 amd massively reduced boiler's on time as response to gas prices.
TBH, as others have said, I don't think Legionella is that widespread in the UK.
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>>
>> TBH, as others have said, I don't think Legionella is that widespread in the UK.
>>
...that's because people run their HW at 60C... ;-)
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Is yours all mains pressure, or is your cylinder fed from a dead pigeon tank in the loft? It seems to me that the latter poses much more of a risk than the former.
Our HW is set to 48. By default, at 3am every Friday it would use the electric immersion heater to raise the temp to 65 for 2 hours. This used an additional 4kWh every week, so I have set it to 62 every 3 weeks.
But I can't really see there's much chance of incubating legionella. It comes off the mains so there's no reservoir of warm water in the loft incubating whatever falls into it. How could it get in there?
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Dead pigeon tank in the loft. Which reminds me, I'm overdue putting some stuff in to keep corrosion to min.
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>> Dead pigeon tank in the loft. Which reminds me, I'm overdue putting some stuff in
>> to keep corrosion to min.
Not in the header tank for the hot water, I hope? But it should have a cover on it.
If you mean a header for the heating circuit then yes that's where you chuck the Fernox in.
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18 months ago my old boiler was replaced by a combi ( Intergas Eco RF)..goodbye HW cylinder ( where I now hang my sleeping bags) and loft tanks.
I only turn the boiler on when I want a shower and find it easier to boil a pan of water for occasional washing up. For the first time, having read this thread, I noticed a ‘75’ on the boiler display whilst the boiler was on this AM. If it’s the water temp, guess I’ll turn it down...
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About 40 years ago I replaced the header tank and the 50 gallon storage tanks.
Of course I also fitted a Bylaw 30 kit so nowt gets in the tank except water and sand from waterboard repairing the many major pipes in our area.
Hot water is at a suitable temperature for me so after so many decades I am not worried about
bugs in the water
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During the Covid lockdown the schools were closed . The normal cycle of flushing the school heating, hot water etc was stopped. Re-opening schools was delayed for anything from a few days to a week - testing showed Legionella which required work, re-testing and then possible further treatment where necessary.
A few people died in the East of Edinburgh 5/6 years ago by walking in the street - a college, a drug manufacturer, brewery were all possible causes - they all put their hands up "Not us" we rigorously clean down AC, heat exchangers, heating systems etc etc
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For those of you worried about Legionella have you checked what temperature the water is actually getting to or are you trusting the accuracy of the thermostat?
My old (original) Honeywell thermostat was set to 60deg but was actually switching between 45 and 50deg (measured at the top outlet of the tank).
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I do, I have a digital display probe tucked on the the tank. I use that to control the temp, not the stupid fiddly badly marked stat control knob.
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Even if the water in the tank is Legionella free, it can develop in shower heads etc. if they are not used regularly. When you get back from holiday, the recommendation is to let it run hot for a couple of minutes before use.
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5 mins if not for used in 14 days is what we are told at work.
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>> 5 mins if not for used in 14 days is what we are told at
>> work.
>>
I don’t sing in the shower so keep my gob shut and don’t drink any of it.
Safe so far :-)
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>> I do, I have a digital display probe tucked on the the tank. I use
>> that to control the temp, not the stupid fiddly badly marked stat control knob.
>>
How did you get a temp probe fitted and sealed in the tank? I think the control knob on mine is vague at best, when at min it does not align with the end stop.
Last edited by: sooty123 on Thu 3 Aug 23 at 19:56
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Thanks for the range of answers, all. I didn’t mention I run mine at, according to the fiddly thermostat on the tank, a mere 45 degrees.
I don’t know whether the Nest protection thing is able to magically override that, but if it is, I can’t see how. I think it must just run at 45 for a long time, which seems pretty pointless.
I use oil, not gas, and don’t have solar, by the way, in answer to a query from Smokie.
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British Gas / Centrica to discontinue HIVE products- some already have been cut and others will be discontinued in August 2025
Security Cameras already cut off - the rest to follow
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Legionella - smokie
