My Nest Thermostat randomly switches my hot water on

[Bob99]

So I fitted the Nest before Xmas last year. Heating system works perfectly. Hot water responds to all scheduled requests but also randomly comes on during the week. Late at night, lunchtime, different days. Cant tie it in to any other activity in the house.
When the water switches itself On, the app tells me it’s “off”. I need to manually switch the boiler off. This has been going on for months to the point where I have removed all scheduled requests and only use Boost requests. I’ve tried going thru “Reset All” several times but it doesn’t change anything. 
I feel I’ve investigated this to the point where Ive proven the Nest is faulty and I’m going to return it for a replacement. Having installed this **bleep** thing for efficiency purposes it has cost me money in unrequested gas consumption. 

[Dazza429]

We’ve had our NEST for 4 years now (2nd gen) and ours has just started doing exactly the same. Hot water randomly comes on but shows off on the thermostat. Solution much appreciated please. Darryl

[Bob99]

I still have the problem. Expect it’s either the Nest hub or possibly an earthing fault in the switching circuit. 

[Big-Al]

I have a Gen 3 nest recently installed and it also is randomly turning on the boiler to heat the water. The only way I can stop it is to turn the hot water tank thermostat to minimum and this turns off the boiler. I have turned off the the water scheduling and the legionaries bacteria prevention feature and it still randomly turns on.   Any ideas how to fix this. 

[Bob99]

The tank thermostat doesn’t seem to affect my system. Switching seems entirely random. Sorry can’t be more help. 

[Big-Al]

Have you disabled the bacterial prevention feature?

[Bob99]

It’s a 20+ Yr old system. No anti bacteria feature that I’m aware of. 

[Dazza429]

I posted elsewhere on the forums, I got in touch with NEST technical help. It’s early days but disabling the bacteria prevention feature seems to have fixed it for me. But if doing that still hasn’t fixed yours, it’s costly, but the item I replaced before this was the Hot Water zone valve, I convinced myself it was stuck open and therefore sending a signal to fire up the boiler, maybe look to troubleshoot that? My system is “S” plan.

[Big-Al]

It is anew boiler installation so I suspect it is a setup issue, although if there is a fault that would be covered by warranty. I have just gone through the bacterial prevention disable process again and this time I also did a reset so hopefully that will fix it. 

[Bob99]

My system is 20+ years old. There is no anti bacteria feature to disable. 

[Big-Al]

Bob99 - it’s a nest thermostat feature nothing to do with the boiler. See link below 

https://support.google.com/googlenest/answer/9256656?hl=en-GB#zippy=%2Cturn-bacteria-prevention-on-o...

[Dazza429]

I’ve just read that link and realise now exactly what happened. We had our hot water come on for two hours in the morning and two in the evening. To save money about a month ago I changed them to an hour, which is one of the conditions of bacterial protection. My money saving exercise cost me £96 for a new valve!!……..I’m sure it was about to fail😂

[Bob99]

Thanks, didn’t realise. Will try and let u know. 

[Bob99]

There’s only two of us in the house so I set for one hour in the morning and boost later if needed. Bacteria was set on so prob was the root cause of the random triggers. Have set to off now. Will let u know how things go over the next week….unless we are hospitalised with legionnaires of course 🤪. Many thanks for your help. 

[Dazza429]

yes, we could become hospital bedmates , and bore all the other patients with hot water/boiler system stories😂

[Bob99]

Looks like switching the Bacteria setting to off has fixed the problem. Why they default this to ON is beyond me. 

[Big-Al]

I am glad it fixed your problem. It is ridiculous that the default is on and it is not obvious how to turn it off.

[Dazza429]

Excellent. In my case it wasn’t defaulted to on, in reducing my hot water schedule below 2 hours caused it to to activate. Still annoying though🙄

[Gasman05]

Thank you for this.  Have the exact same problem and just gone and disabled the bacteria function.   

[Chrissie1]

Thankyou for the link it now comfirms what i thought that that's what it was doing.

[Dazza429]

Big-Al, two other things they got me to do while sorting mine, turn-off auto-scheduling and erase the hot water schedule and then re-enter it. No idea why but just a couple more things to try before getting the installer back under warranty. Good luck

[Bob99]

I tried this several times but had no effect. 

[Dazza429]

I think I have exhausted my sum total knowledge on this subject, sorry

[Bob99]

Thx anyway. Big Al may have nailed it. Bacteria settings. It’s like a bloody video game with hidden secrets and cookies. 

[Big-Al]

Hi, so I called the installing electrician in and he identified the issue as a hardware fault on the heat link so they will replace that under warranty. 

Al

[Dazza429]

Pleased you got it fixed, and a cheap option too😉

[Bob99]

It’s a good call but it has been replaced in the last couple of years. Maybe time to replace it again. Covered under a maintenance contract so no cost to me. 

[Dazza429]

Bob99, my experience and research, Honeywell may be slightly more expensive but you get what you pay for, far superior. If yours is Drayton, there is a chance that it could well have failed again!

[Jeran]

Hey there Bob99,

I'm just checking up on this thread, did you have any more questions or need any additional help? 

Thank you for helping out on this thread, everyone!

Best regards,
Jeran
 

[Jeran]

Hey there Bob99,

Did you have any more questions or need any additional help? 

Thank you,
Jeran
 

[Jeran]

Hey there,

Did you have any more questions or need any additional help? If not, I'll go ahead and lock up this thread in 24 hours.

Just checking up,
Jeran
 

[Bob99]

Problem fixed.  Bacteria setting defaults “On” causing random switching of hot water. Absolutely bonkers idea. Nearly caused me to remove the device and send it back. 

[Big-Al]

I am glad you got it fixed. Personally I will never buy a Google device again. I have had a device with a hardware fault on it from new. The support desk wanted a load of info including diagrams of how the device was wired and the diagnostics that were run by the installer. And now after agreeing that it is faulty they want me to set up a Google pay account with my credit cards details in it before sending a replacement. 😡😡😡😡

[Dazza429]

I’m happy for you to close it, can’t speak for the other contributors of course.