Bacteria Prevention - how does it work when solar panels also heat the water?

[Phil_G]

The hot water on my Nest is turned off at the moment because I'm heating my water with solar panels, but I've discovered that bacteria prevention is turning it on every couple of days as it thinks it hasn't been heated. The Nest help is a bit sparse on the function so I'm seeking advice on how it works, before deciding what to do. The help function implies it turns on for two hours every 48 hours. Does this still happen if the water is fully heated? If it is less than fully heated, does it just turn on until the immersion thermostat is fully heated, which may be less than two hours? Or does it just heat the water for two hours regardless?

[Phil_G]

In case anyone else has this question, Google Support have told me that bacteria prevention overrides everything. So if your hot water is being heated by panels, and is turned off at the Nest, the Nest will put 2 hours of power into the tank every 2 days. As the water will already be hot you will get some very hot water unless you turn off the feature.

[Jenelyn_O]

Hi Phil_G,

Thanks for reaching out. I'm sorry for the delay. A few questions: what type of Nest Thermostat do you have? You can visit this link to check what type of thermostat you have. Also, in what states are you located?

Best,

Jenelyn

[Jenelyn_O]

Hi there,

Checking if you still need help. Please let me know, as I'll be willing to assist you further. 

Thanks,

Jenelyn

[Phil_G]

Yes I still need advice but I will not be able to answer your question about the type of Nest for a week as I’m away from home. 

[Markjosephp]

Hello everyone,

I wanted to ensure that everything was covered here.

Thanks for the help here, Jenelyn.

@Phil_G, got it. I did find a helpful article that would tell more about how the Nest Thermostat helps prevent Legionella bacteria. Let us know if that helps.

Best regards,
Mark

[Markjosephp]

Hello Phil_G,

Checking back in — how's it going? Still need our help?

Thanks,

Mark

[Phil_G]

Thanks for responding. I'm unable to look at this until next week so I'll get back to you then.

[Markjosephp]

Hi there,

Got it. I'll leave this thread open whenever you're available. So please keep us posted on how it goes, as we would be glad to know what the result will be.

Thanks,
Mark

[Phil_G]

Hi. To answer the questions from Jenelyn, my Nest has a small screen - but it's 5.2 cm rather than the 4.57 described in the link for a 2nd gen. However, I see from the article that this feature is only on the 3rd gen, so that's confusing. Is there such a thing as a small screen 3rd gen? I'm located in the UK.

I understand how the feature works - it is unaware of the solar source so it will turn on and heat up the water if the gas hasn't been on for 48 hours, despite the fact that the solar panels may have heated the water. My remaining question is: does the feature respect the immersion's temperature setting? So if the water is hot due to the solar panels and the bacteria prevention turns on as the Nest hasn't heated the water for 48 hours, does it switch off as soon as the water reaches the thermostat temperature setting on the immersion (60 degree +)? This appears to happen, but I'd like confirmation please.