3rd generation nest learning thermostat

[Mitchmort]

Just found out about the legionella concept. How long does it come on for in this mode? Although I have set my hot water to come on one hour in the morning and one hour at night, it still kicks in.

What can be done?

[Jhonleanmel]

Hi Mitchmort,

Most hot water systems are compatible with the Nest thermostat’s Bacteria Prevention mode, so it’s recommended to keep it on. But it can be turned off if you are away for an extended period of time, such as a holiday home that is only used during the summer.

To check if Hot Water is set to on/off:

1. Press the thermostat ring to bring up the Quick View menu
2. Select Settings .
3. Select Equipment.
4. Choose Pro Setup.
5. Select System boiler.
6. Select Hot Water control On/Off.

To turn off Bacteria Prevention:

1. Press the thermostat ring to bring up the Quick View menu
2. Select Settings .
3. Select Equipment and Continue.
4. Choose Bacteria Prevention.
5. Select Enable or disable Bacteria Prevention.

Keep us posted.

Best,

Mel

[Mitchmort]

Thanks Mel!

I have in the last two days set the boiler to operate 1 hour in the morning and two at night. This seems to have stopped the spurious boiler activities.

Still interested to find out if you reduce the timings and the boiler kicks in on legionella protection, how long does it come on for. Is it time or temperature related?

[Jhonleanmel]

Hi Mitchmort,

Legionella bacteria can develop in water that has been exposed to impurities like rust, algae, and limescale, in temperatures between 20 and 45 °C. The bacteria are dormant below 20 °C and do not survive above 60 °C.

Bacteria Prevention is an exclusive feature of 3rd Gen Nest Learning Thermostats (NLT). Bacteria Prevention mode will activate if the domestic water hasn’t been heated for at least two consecutive hours in the last 48 hours. This can happen if there is a gap of more than 48 hours in the hot water heating schedule or if you are away from home for longer than 48 hours. For instance, if you have a second home or holiday home and only need hot water for weekends, you can create a hot water schedule for Saturday and Sunday, and the Bacteria Prevention mode will automatically heat the hot water tank during the week.

Best,

Mel

[Jake]

Hey Mitchmort,

I wanted to check in and see if you managed to see Mel's post. Please let me know if you have any questions from here. I would be happy to assist, and make sure you are good to go.

Best regards,
Jake

[Mitchmort]

Hi Jake! Thanks to you and Mel! For a week now the Nest has not come on for the legionella setting.

Hot water set for one hour in the morning and two hours for late afternoon.

I wanted to know if you have low settings and the legionella setting kicks in, is it based on time our temperature? Does it depend on boiler settings?

I have shared my information with two boiler engineers who were stumped by the then spurious workings of my boiler. Modulating valve and cylinder stat replaced during this period! 
So pleased it's sorted as I was contemplating a new boiler at £3500! 
Just another question, when does the start / app light up in orange? It seems to modulate between the on/off of the orange for hot water. So on a two hour timing for hot water, on the app, sometimes orange sometimes not? Not had a chance yet to observe it when my heating is turned on!