I had to rip it from the wall. It was one of the most frustrating technology experiences I've had in years, and I'll have to see something REALLY compelling if I'm ever to try home automation again.
It was a fascinating discussion all around with some interesting lessons:
1) No one seems to consider a thermostat as a device which requires safety controls.
2) The built-in safety controls on a consumer HVAC unit tend to be insufficient & kick in well after temperatures in a home can get dangerously hot, if they kick in at all.
3) Because of the custom nature of every HVAC install, with more air going to certain rooms than others, it's not possible to draw any conclusion about the nature of whether a situation with a rogue thermostat can become deadly.
4) It appears a large majority of digital thermostats are built to a "toy grade" standard.
This is likely a topic space that doesn't get enough attention and I hope I opened a few eyes over at Spark. The fact is, such incidents don't happen often so they simply don't get the attention. This is unfortunate, because with the state of modern safety systems and designs an out of control thermostat is something that should never happen.
It worked just fine for heat -- although I later found out that every time it turned on my heat pump it was activating the emergency heat. I tried finding a way to get the unit to be okay with ramping up the temperature over a longer period of time, but that setting was not exposed in their UI. All I wanted was to say "I don't really care what temperature the house is while I'm gone so long as it never goes below 55F or above 80F, but I want you to make sure that when I arrive home at 6PM the temperature has reached the point I set". But...alas, the unit never figured that out. The "learning mode" never actually did anything, no matter what I tried.
Fortunately I was able to get a full refund on the devices from Amazon.
It just said "heat" when the furnace was on.
EDIT: corrected that whole last sentence. It made no sense.
I don't know anything about nest, maybe it displays that in other situations.
Instead of A/C, the unit activated heating. So the temperature kept rising even further beyond the setpoint. So, more heat.
Positive feedback -- exactly what I didn't want.
(I'm presuming enough QC in the manufacturing that improper wiring is the most common trigger of positive feedback)
Have you gone far enough into it to compare how the wires are hooked up on the heat pump side to the nest diagram? Not trying to heckle you about it, it's a puzzle, it must be solved.
I agree with you. I love solving puzzles, that's why I'm an engineer. But I had to balance solving this puzzle with the ongoing puzzle of maintaining domestic harmony. My then-pregnant-wife insisted I get the system working properly ASAP. The best way to do that was to reinstall the Honeywell -- the system worked properly within 15 minutes. As life circumstances dictated that I was away from home for most of the time -- and we moved a couple of months later, the best solution was to get a refund.
Did I have some wiring wrong? Most likely.
Not to beat my credentials against my chest, or to imply that they mean that I could not have possibly made an error... I have engineering degrees and have done a lot of instrumentation system design work. Figuring out how to wire up strange sensors to an existing system is something I do all the time. If I had this kind of difficulty, what kinds of problems are ordinary people having? Or maybe it just reinforces the aircraft industry joke that "you shouldn't let engineers touch tools, they'll break something".
I appreciate the company's consumer electronics mindset, but they need to take the business of running HVAC systems more seriously.
My "dumb" thermostat is back on the wall and successfully running my heating system (to the schedule I've programmed it) as it's done for years.
In the UK, the control circuit is on the mains; close the circuit, the furnace is on.
When I first got them, they worked great in the sumemrtime. No complaints. But they were bloody awful for me in the winter:
* Nest would, randomly, refuse to turn on AUX heat. I woke up one morning and my house was in the upper 50s (the set temperature was 68) and Nest was just sitting there trying to run the heat pump instead of turning on AUX when it wasn't keeping up. At first I thought there was something wrong with my HVAC system, but I've had two different people look my system over, on three different occasions, and found everything working properly. Nest was just refusing to turn on AUX.
The first time it happened it was in the single digits outside and Nest let my house get into the upper 50s (temperature was set at 68, and it was still trying to run the heat pump even though it was in the single freaking digits outside). I finally took Nest off the wall and manually shorted the aux heat on - I didn't want the house to get any colder while we "troubleshooted" it, and Nest was just refusing, no matter how I adjusted it, to turn the aux heat on and warm the house back up.
* Other times, it would use AUX when it doesn't need it. It was 37 outside once, and nest was burning AUX like crazy when the heat pump was having no problems keeping up. I had a nearly $400 power bill last January. Now, in fairness, it was very cold that month, but Nest using AUX when it shouldn't was a big contributor.
* For instance, you can't directly set the AUX lockout any lower than 35 degrees (more on this in a minute) when, for my house, it probably needs to be around 26. You can also only set certain things from the thermostat itself.
* They are very difficult to troubleshoot. How do you manually turn on AUX heat to test if it's even working at all? As far as I can tell, you can't! The only way we were able to test it is to take the thing off the wall and manually short the wires together (and, of course, it worked fine).
This is not some weird setup either. It's a standard heat pump with electric heat strips for aux heat, that's only about 4 years old. Where I live, this is the absolute most common form of heating. Because I can take the thermostat off the wall and short the wires together to turn aux on (and because I've had two different HVAC contractors check my system), I'm fairly certain the problem is not my HVAC system.
The biggest problem was, after three times of waking up to a cold house, I had a very difficult time trust them. I had an infant in the house, and for something that I'm not supposed to have to think about, I was spending an inordinate amount of time worrying about.
So at one point I replaced one of them with a Honeywell (not the Lyric, one of the touchscreen models). And it worked fine for the rest of winter and was much less crazy to deal with, but once summer rolled around the Honeywell wouldn't turn my air conditioning on! In troubleshooting it, we found that the Honeywell was defective and wasn't putting enough voltage to activate the reversing valve. So the heat pump was still running.
So I ended up putting the Nest back on for the summer, but spent a lot of time reading the Nest forums. Apparently problems with AUX heat are SUPER common with Nests (just Google "nest aux heat" to see tons of complaints).
There's a hack that that you can go through (detailed here: https://community.nest.com/ideas/1144#comment-7150) that allows you to set the lockout to a lower temperature. Which I did eventually set to 26. And, sidenote, I really hope they don't close this hole, because a lot of people are relying on it.
So far this winter, no problems. The hack seems to be holding. I haven't woken up to a cold house yet, and Nest is only using AUX when it should. And my power bills are running 25% less than the year before thanks to Nest not constantly using AUX heat.
I'm still very wary of them. If I wake up to a cold house again, they are going right in the trash can.
I don't own a Nest thermostat myself, but was browsing their blog out of curiosity after reading this story, and it sounds like the latest software update includes a System Test mode:
https://nest.com/ca/blog/2014/11/04/whats-in-the-4-3-softwar...