Nest bacteria prevention

psd99 · 13 Aug 2018 at 10:54

I wondered why the boiler had been turning on randomly through the day with a little yellow flame on the nest display.

A quick google suggests that the nest has a built in bacteria prevention program and that this is normal.

I got the hot water set to run at 5am to 6am and 5pm to 6pm daily.

Is it worth me turning the bacteria prevention off? Or shall I leave it running? what did you nest people do?

VincentHanna · 13 Aug 2018 at 11:02

Well...if you like the idea of bacteria in your water and want to risk it, feel free!

psd99 · 13 Aug 2018 at 11:14

VincentHanna said:
Well...if you like the idea of bacteria in your water and want to risk it, feel free!

okay but what are the chances of this happening in a residential property?

Which other heating controls actually do this? If it is that dangerous and risky then why are not all systems having this feature?

VincentHanna · 13 Aug 2018 at 11:17

https://nest.com/uk/support/article/How-does-the-Nest-Thermostat-help-prevent-Legionella-bacteria

lude1962 · 13 Aug 2018 at 11:30

Turn it off.

touch · 13 Aug 2018 at 11:43

VincentHanna said:
https://nest.com/uk/support/article/How-does-the-Nest-Thermostat-help-prevent-Legionella-bacteria

From this link:
"The 3rd-gen Nest Thermostat’s Bacteria Prevention mode will be activated if your domestic water hasn’t been heated for at least 2 consecutive hours in the last 48 hours."

Presumably it needs 2 hours heating to effectively kill the bacteria? I'd just change of your current hot water periods to a 2 hour slot rather than 1 hour (4am-6am or 4pm-6pm).

psd99 · 13 Aug 2018 at 11:46

touch said:
From this link:
"The 3rd-gen Nest Thermostat’s Bacteria Prevention mode will be activated if your domestic water hasn’t been heated for at least 2 consecutive hours in the last 48 hours."

Presumably it needs 2 hours heating to effectively kill the bacteria? I'd just change of your current hot water periods to a 2 hour slot rather than 1 hour (4am-6am or 4pm-6pm).

that is a good suggestion,

but would 4 hours per day be overkill?

touch · 13 Aug 2018 at 11:50

psd99 said:
that is a good suggestion,

but would 4 hours per day be overkill?

He wouldn't need to change both, just one of them.

Either:
4am-6am and 5pm-6pm
or
5am-6am and 4pm-6pm

Both would give a continuous 2 hour heating period every 24 hours so it should stop the bacteria prevention from kicking in.

edit: actually, it needs 2 hours in a 48 hour period, so you could just change the schedule to include 2 hours every second day instead

psd99 · 13 Aug 2018 at 12:12

touch said:
He wouldn't need to change both, just one of them.

Either:
4am-6am and 5pm-6pm
or
5am-6am and 4pm-6pm

Both would give a continuous 2 hour heating period every 24 hours so it should stop the bacteria prevention from kicking in.

edit: actually, it needs 2 hours in a 48 hour period, so you could just change the schedule to include 2 hours every second day instead

Good point but my plumber told me something I had zero idea about.

basically sometimes the hot water will not come on, he says that is normal because probably there is enough hot water in the 250L tank
so the system's thermostat stops the water from turning on. Is this true?

So like for instance yesterday at 5pm the water came on for like 30 minutes then turned off, but even if I set the schedule as suggested it will be the same outcome?

mght as well just turn the feature off then!

Hotwired · 13 Aug 2018 at 12:38

VincentHanna said:
Well...if you like the idea of bacteria in your water and want to risk it, feel free!

There is such thing as considering the reality of the risk.

Or do you inconvenience yourself in some way for every risk you are told about.

Dis86 · 13 Aug 2018 at 12:42

Hotwired said:
There is such thing as considering the reality of the risk.

Or do you inconvenience yourself in some way for every risk you are told about.

What's a bit of legionella between friends, eh?

Diddums · 13 Aug 2018 at 12:48

I'm fortunate enough to be in the position of being aware of the risks of legionella and legionnaire's disease so seeing threads like this is a real eye opener.

Short version: No. Leave it on.

Long version: If you turn it off, you run a very real risk of cultivating legionella bacteria. They grow between 38-43deg celsius which is obviously the perfect temperature of a boiler that's cooling down. Legionnaires is only contracted via inhalation so you can be having a nice shower one day and inhaling deadly bacteria which has killed many people in the past.

Here's the HSE's PDF on it:

http://www.hse.gov.uk/pUbns/priced/l8.pdf

Ugley_Matt · 13 Aug 2018 at 12:55

Think about it. Has anyone you known in the past ever had an issue with bacteria in their domestic water? The fact that your smart boiler tells you this suggests ist not really an issue and just turn it off.

Shure · 13 Aug 2018 at 13:03

Check what your cylinder stat is set to. If it is too low then the amount of time the boiler is firing up will be irrelevant.
I think it should be st to at least 55 degrees.

EDIT: Unless Nest can overide the stat, I'm not familiar with Nest

psd99 · 13 Aug 2018 at 13:03

Ugley_Matt said:
Think about it. Has anyone you known in the past ever had an issue with bacteria in their domestic water? The fact that your smart boiler tells you this suggests ist not really an issue and just turn it off.

that is what I'm thinking about

if it is that serious why isn't it a law to have EVERY thermostat in the UK do this automatically!?

psd99 · 13 Aug 2018 at 13:05

Shure said:
Check what your cylinder stat is set to. If it is too low then the amount of time the boiler is firing up will be irrelevant.
I think it should be st to at least 55 degrees.

EDIT: Unless Nest can overide the stat, I'm not familiar with Nest

think the water on the tank is set on the megaflow itself by two seperate thermostats.

Hotwired · 13 Aug 2018 at 13:10

Diddums said:
I'm fortunate enough to be in the position of being aware of the risks of legionella and legionnaire's disease so seeing threads like this is a real eye opener.

Short version: No. Leave it on.

Long version: If you turn it off, you run a very real risk of cultivating legionella bacteria. They grow between 38-43deg celsius which is obviously the perfect temperature of a boiler that's cooling down. Legionnaires is only contracted via inhalation so you can be having a nice shower one day and inhaling deadly bacteria which has killed many people in the past.

Here's the HSE's PDF on it:

http://www.hse.gov.uk/pUbns/priced/l8.pdf

Excellent so you're aware you should do a proper risk assessment rather than fearmonger.

Thus coming to a proper decision taking into account the specific circumstances.

Diddums · 13 Aug 2018 at 13:20

Hotwired said:
Excellent so you're aware you should do a proper risk assessment rather than fearmonger.

Thus coming to a proper decision taking into account the specific circumstances.

I don't take risks.

Tom_ed1987 · 13 Aug 2018 at 13:55

Legionella mitigation in a domestic hot water system sounds totally unnecessary.

i'd leave it off & likely extend the lifetime of your boiler in the process.

Firestar_3x · 13 Aug 2018 at 13:56

You should be heating the hot water tank to around 65oC once a day anyway.