Hot water is on when not requested by schedule

[Bill29]

On a number of occasions my boiler has turned on, with the valves set to heat the hot water (but not the central heating) when this should NOT be happening. The Nest thermostat shows that both heating and hot water should be off, and the Nest App (iOS) agrees - both should be off. When this occurs, an icon appears on the Nest thermostat display that is not described on the help pages: it's a yellow / sandy coloured circle with a black drop-shape inside it and it appears where the green ECO leaf would be. This has been consistently observed on the occasions where I caught the boiler in this anomalous state. I have a photograph showing the icon but can't figure out how to attach a file to this post.

What is the mode that the thermostat is in when this is happening? How do I stop it from happening (I don't need hot water - I already have most of a tank full, and the next scheduled hot-water heating event will give me the top-up that I want)?

[Bill29]

May have an explanation:

The icon is "bacteria prevention" and this mode may have become enabled when I recently changed my hot water schedule - it is now on from 0600 to 0630 every day, which is sufficient to get me through the day nicely. But the help pages state that if the hot water is not heated for two consecutive hours within a 48 hour period then the thermostat will run Bacteria Prevention.

It seems I have options:

1) turn this feature off on the thermostat (which is what you are recommended to do if you're going to leave the house empty for extended periods)

2) change my schedule back to include a 2 hour period at least every other day

3) accept that the thermostat will run these spurious heating events (pretty much the same as option 2, I think, but not at a time of my choosing)

Anyone else seen this behaviour? And if so, what did you do about it?

[Frustratedddd · Accepted solution]

The easiest is dissable Bacteria setting. The main reason for this is not using the hot water function, but if you live in the house 24/7 then just dissable. Mine has been dissabled since the 3rd Gen was launched, and no issues.

This is a common issue, and amazed a Forum Mod has not been to your rescue!!

[Bill29]

Thanks for your reply. I’m trying a schedule that avoids the problem but if I end up with too much hot water I will disable the mode and refine the schedule again. Last summer I just ran my immersion heater and turned off my boiler completely. I might try that but as I have a new electricity tariff I will need a time switch to use the cheap rates