Unexplained intermittent gas usage

[MarionC]

We use a Nest, installed in Feb 2024, to control our gas boiler, for heating and hot water. According to the meter readings supplied by Octopus, our gas supplier, we are using small quantities of gas every 50 hours - but only while we are away, when the Nest is set to frost settings and hot water is turned off.

Looking at the readings I've downloaded this intermittent usage doesn't happen when we are at home and using gas regularly for heating and cooking.  It also hasn't happened on the one occasion we went away and turned off the gas supply at the meter, so there was no gas coming into the house. Octopus insists that there is a leaking device somewhere in the house. We only have two gas devices  - a gas hob and the boiler, controlled by the Nest. Is it possible that the Nest is causing this intermittent gas consumption when everything is meant to be off?

[GBD]

In my experience with boilers, unless you completely remove power from them, they will still fire intermittently to keep the water in the reservoir hot.

[MarionC]

Thanks. By reservoir, do you mean the water in the boiler itself? It's not a combi-boiler, so we have a separate hot water tank. But the Nest is set not to heat the water in that while we are away.

[GBD]

Yes the water in the boiler itself. Your boiler should have a low set temperature and high set temperature. Whenever the temperature of it's internal tank falls below the low set temperature, it will fire to raise the water temperature up to the high set temperature.

[luciaaa]

Hi, @MarionC,

Thank you so much for posting in the community. I'm sorry to hear about the intermittent gas consumption you're experiencing with your system. I’m happy to assist you. 

To better assist you, I have some questions related to your thermostat:

• What type of thermostat do you have? 
• Are you located in the US, Canada, or Europe?
• When did the issue start?

In the meantime, while you're at home, I recommend turning off the temperature at the thermostat and letting me know if the gas usage continues even when the temperature is completely off.

Keep me posted.

Best regards, 

Ana. 

[MarionC · Accepted solution]

Thanks to everyone who has replied. After much internet searching (if only we had known which key words to use!) we have discovered that our 3rd Generation Nest has a 'bacteria prevention' setting, designed to prevent Legionnaires Disease it seems. It will heat the water for about two hours, whenever it detects no activity for 48 hours. Ours was firing at 7pm the evening after we had left home, when it would normally be due to heat the water if we had been at home. So the problem is now sorted. It seems that our energy supplier is completely unaware of this setting, which is why they kept insisting we had a leaking gas appliance.

Ana - for information, we're in the UK.

The relevant Google article is here: https://support.google.com/googlenest/answer/9256656?hl=en

[luciaaa]

Hi, @MarionC,

Thanks for following up. I truly appreciate all the effort you put in to resolve this. I'm glad to hear the situation is finally sorted.

I'm grateful you followed the steps and shared the article. It will be incredibly helpful for others facing the same inconvenience.

Please don't hesitate to reach out if you have any further questions.

Best regards,

Ana.