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True Radiant timing not as described

Community Member

I installed a Nest Learning Thermostat a few weeks ago to control our steam heat system, which uses radiators.

My understanding of the True Radiant function is that the thermostat learns how long it takes to reach target temperature and for how long the temperature will rise after the boiler is shut off. Based on that, it will start the boiler before a higher temperature set point in the morning so the temperature is at least close to target at the scheduled time.

After several weeks, my thermostat may start the boiler 30 minutes early, but still takes another hour or so to reach the target. Even worse, approaching the night time set back, it will still start a heating cycle less than 20 minutes before the set back goes into effect, with no chance of the system warming up enough to have an effect. A total waste of energy.

Settings are:

Auto-Schedule: Off
Time-to-Temp: Ready
True Radiant: On, Ready

What am I missing here? 


Community Specialist
Community Specialist

Hi Phoibos,

Thanks for posting and sorry for the delay ― let's get this sorted out.

A few questions: since when has this been happening? Also, what troubleshooting steps have you done so far?


This seems to never have worked right. I’ve gone as far as removing the thermostat from the account and resetting it to factory settings but that doesn’t seem to clear the learned behavior. 
In the History view, tapping on a temperature will show a message about starting early to reach the temperature at x:xx but the graph shows it didn’t. 

I should add that I am using a temperature sensor in a different room to trigger the system, not the temperature at the thermostat. That shouldn’t affect how the system works but who knows. 

Community Specialist
Community Specialist

Hi Phoibos,

I'm sorry to hear that you're still having an issue with your Nest Learning Thermostat. We'd like to take a deeper look into this — could you fill out this form and let us know once you're done?


Just entered all the same information again in that form. 

Is someone actually going to address this issue now?

Wow. I did receive a response and it didn’t address anything I wrote. If this is the customer support you provide, I’m sorry that I invested in a Nest thermostat. 

Community Member

I have a separate thread in the forum regarding the exact same problem. The true radiant feature does not work. I’ve done enough research, and what I’ve observed, is the fact that it never goes into learning mode. The true radiant feature says on/ready, and never goes to on/learning mode. My biggest problem is the fact that it’s overheating my house by 2° to 3°. The true radiant feature was also to learn how long it takes the system to reach the target temperature and then turn off the heat early. It’s actually running my boiler 15 to 18 minutes beyond the target temperature. Totally burning more fuel than necessary. It is a serious software issue. If you search this issue on the Internet, you’ll find that there are numerous complaints in this forum as well as other places, regarding the true radiant feature not working. And it’s also been an ongoing issue for years. I am also waiting on a response after filling out the form as instructed. This issue needs to be reviewed at their engineering level. I’m not so hopeful that this will happen.  Looks like I’m stuck with a very expensive hockey puck at this point. I’m probably gonna go out and buy a cheap Honeywell thermostat.

Community Member

I agree, the True Radiant feature is not working as described. I believe it is learning a little but not as intended. For example, my heat does turn on a but earlier than the scheduled rise. But only maybe 15 minutes. It takes 30 minutes alone to get the radiators to warm up, so the target is reached about 1 to 1 1/2 hours late. It appears to shut off heating a bit early so the residual heat can do the rest. But the biggest complaint is that it starts heating within the last half hour before the nightly fallback, with no chance to get radiators to warm up (and no need). 
I’m still waiting to hear back but since more than a week has passed, I’m not terribly optimistic. 

Yes, sounds like yours is partially working. I am located in US and this feature doesn’t work at all. I even bought a second third generation thermostat to test and it behave the exact same way. The true radiant feature would not work at all. Where are you located? From what I have read the nest thermostats in Europe, are different in terms of how they were installed.

In the US, same as you. 
I tried a full reset, I tried with and without self-learning turned on. I adjusted pre-heat time duration. Nothing ever made a difference. 
This looks like a real bug to me. But given how unresponsive their customer service is, I suspect they don’t care much. Google probably acquired Nest because the look fits, and then told them to save money on support and sustaining engineering. 
Did you notice that they seem to close the ticket every time they send you a response, no matter what it is? Even if it’s a follow-up question? That makes their open ticket count look real good…

This is very interesting that yours partially works and mine hasn’t worked at all including with the second one I bought and returned. I also had reset them numerous times, but could not get the true radiant feature to learn. Let’s move our conversation off of this forum I’d like to speak with you outside of this. Email me “”had to use the word at for the @symbol, they have it, so you can’t post any email addresses here. 

Well, sounds like yours is partially working. That’s better than mine, which doesn’t work at all. Out of curiosity what part of the world are you located in? The European version of this thermostat hooks up differently than the one I have, which is North American model.(I’m in the US) I even went out and bought a second third GEN thermostat to test and it did the exact same thing. The true radiant feature did not work as advertised and it consistently overheated my house.