Thermostat unreliable temp readings, temp gets stuck

Have been having an issue for at least a year or more where the thermostat will read the incorrect temp causing hvac to continue running far past intended target.

An example: I was working upstairs this morning for a couple hours (different thermostat and hvac) and when I came down the living room felt really warm and the heat was still running, so I checked the accurite on the fridge and it says its 78 (I don’t consider it perfectly accurate due to it’s location, but its close). I check the downstairs thermostat, T-3000 and it reads 69 with a target of 71. Suspecting I already know the issue and this to be wrong I pull the thermostat off the wall and pull the batteries, replace batteries, put back on wall. Stat now reads temp as 77 and heat turns off. About an hour later the same exercise repeats.

As mentioned this has been happening for a year or more and happens with both heat and cool cycles where the read temp seems to just get stuck in the stat and the system runs nonstop trying to reach the target. I originally had T-2000 thermostats, and I am not sure but I believe it was happening to those as well. It did not happen for the years we had Vivint prior to that contract ending and rolling my own system with Surety. The HVAC is the same HVAC we’ve always had downstairs.

I recently replaced the downstairs T-3000 FW 1.2 with another that I bought with FW 1.3 hoping maybe that would help and for a week or two I thought it did, but the issue returned.

Either this is something really common with the ADC thermostats for it to occur across devices, or there is something else going on outside the devices that is causing this. Pulling stat/batteries always fixing immediately, at least for a short while. Schedules, time of day, etc don’t seem to correlate with when it occurs and I’ve looked at all settings that could be related like the humidity management and found nothing enabled with would cause the temp to just be wrong until resetting the stat.

The only other thing I can think of that could be related is that we’ve always had trouble with our system connectivity to ADC, such as the apps not being able to have any effect on the local equipment, like it fails to take temp changes, turn lights off/on, lock doors on command etc and the only fix is usually to reboot the panel which I usually do from the surety site. This issue has followed from a GC2, to GC3, and now GC3e with a new radio in there somewhere due to the LTE switch, so I have just accepted this as a quirk of ADC and learned to live with it.

Please give me some advice?

This issue has followed from a GC2, to GC3, and now GC3e with a new radio in there somewhere due to the LTE switch, so I have just accepted this as a quirk of ADC and learned to live with it.

It’s not. Based on your description it sounds like the thermistor sensor is failing. However the likelihood of this happening across what sounds like 4+ thermostats is nigh 0. (is that right? can you specify how many of what model?) It would be very important to know exactly which models and how many were affected by this issue, definitively.

The HVAC is the same HVAC we’ve always had downstairs

What is the model # of the HVAC?

Of things I meant I’ve just accepted I only referred to the difficulty keeping access to the panel/home from the ADC/cloud side and having to occasionally reboot the panel. The thermostat issue I’m here for is because I couldn’t live with that any longer, I didn’t mean to make it more confusing if I did, just wanted to include that changing panels over the years had no effect either.

Is the thermistor sensor a part of the thermostat itself or the HVAC system? The issue did not occur on the vivint system/thermostat, it was a CT100, but I replaced it with a T-2000 when I switched to Surety. I also had a T-2000 upstairs and I believe I switched (w/ unpair, delete, pair, reprogram etc) them to test if one of them was just bad years ago to no avail. When the T-3000 came out I replaced both thinking finally this would fix it, it has not. So with the latest replacement of the downstairs T-3000 with a new one with FW 1.3 I would say it has followed me across at least 3 maybe 4 thermostats.

It is an outdoor package unit, a Goodman GPH13 36H21AB. It was installed with the house in 2007 so I do expect it is reaching EOL and has had a slow coolant leak since we’ve lived here but other than that it seems to function correctly. If the temperature at the wall stat is somehow derived from the HVAC system that would at least give me some place to investigate.

Something else I just noticed for the first time, idk if this is new or not. In ADC it is showing the downstairs stat wiring as just “Rh C Electric”, it should be the same as the upstairs “Rh W Y C G O Electric”. I just checked the stat itself and it shows the expected wiring (love that feature on the T-3000).

edit hmm after telling ADC to get current values and checking the wiring at the stat, it is now showing the expected wiring in ADC. I have screenshots of it having the wrong wiring showing so I know I’m not crazy lol.

Goodman GPH13 36H21AB

What is the model on the air handler inside?

If the temperature at the wall stat is somehow derived from the HVAC system that would at least give me some place to investigate.

The HVAC is not influencing the temperature reading. The temperature sensor is a part of the thermostat. However, fluctuations in power, under or overpowering the thermostat, might have some unexpected effects. For the temperature sensor to be many degrees off and then be fixed with a reboot on multiple thermostats, there’s not a lot else that makes much sense to me at the moment.

As a test, I would try this:

Delete that downstairs thermostat from the panel (Use the Remove Z-wave Device option in your panel Z-wave menu).
Power off the Air handler/HVAC. Usually your power panel will have a dedicated circuit for it.
With the Air handler powered off, disconnect the C-wire from the thermostat.
Power the system back up and then learn the thermostat into the alarm panel just on battery power (C-wire still disconnected)

After that, test it for a while and see if you notice that issue again on the thermostat. Any change?

From everything I can find since this is an all in one package unit the airhandler portion and the heat pump are both referred to with the same model number, I can’t find any references to a separate model # for the air handler part.

I’ll do this tonight. The bad part is this issue is intermittent, sometimes happening multiple times per day to going weeks without it happening. I will gladly try anything though, just not sure how long to wait to decide if this has helped if the problem doesn’t reoccur.

Thank you so much for your help so far!

Done, testing commenced :slight_smile:

So, good news I guess, at least we don't have to keep waiting to see a result. Removing the C wire didn't help. Been running on battery only since last night and it was working, until 6PM tonight we were out for an hour and came back to the house at 80 degrees while the thermostat thinks it is 71 and is running non stop to the target of 72. Attaching pictures of before and after battery pull on the stat.


Sorry the acurite is hard to read with the contrast from the stat.

I can see that temp, and I am glad we got a definitive result, but it’s no less confusing. I am reaching out to Alarm.com for more info and providing them the HVAC model. It is extremely suspicious for more than one thermostat to experience this, let alone 4. There may indeed be some incompatibility at play.

Just to be 100%, you are sure this exact behavior occurred on all of them (but not the CT100) ?

Can you send a private message with a photo of the general area around the thermostat?

Ok I think I sent you a PM with pictures.

Yes I am positive this exact behavior has been happening on every stat since switching to ADC and positive it never happened with Vivint, we were stuck with them for 4 years on a contract and I’d have sued if they didn’t let us out of the contract with this kind of issue.

Can I change the stat back to using the common wire? I’ll probably switch the upstairs and downstairs thermostats again just for grins since I have to change it anyways.

Yes, you can go ahead and reattach C.

I’m not seeing it above, but just to confirm, is this behavior definitively happening in Cool mode as well, where it cools way past the target? Or just in heat mode?

Ok I didn’t have a chance to reattach the C yet, but the stat did try to cook us alive a couple time this weekend while we were just hanging out, just for some additional data points.

I definitely don’t remember it being an issue any time recently until we switched to heat just a few weeks ago. Of all the times I can remember it being an issue for the past several years I can only remember it being when it was in heat mode.

Of all the times I can remember it being an issue for the past several years I can only remember it being when it was in heat mode.

It’s still strange and clearly something odd going on, but that is good and should help identify this, I expect to find a pattern somewhere.

Do you have a multimeter/voltmeter to test the wiring? What is the voltage between R and C?

I’m not an electrician but I do have a multimeter and a enough knowledge about it to be dangerous. I thought it would test out on DC but it didn’t, it tested as AC at 27.8 volts… Assuming I did it right.

Thank you, yes you would want to test AC. Ok, I am awaiting some feedback from Alarm.com on this for troubleshooting.

Just an update, this just happened 2x again the past 30 minutes. I noticed something I hadn’t before, which may not matter but something I learned, which is that when the stat temp is showing the wrong temp and trying to cook us - the cloud app is showing the correct temps for the stat, it was showing the stat at 76 and both attached temp sensors all showed 75-76 also. I just found it very interesting that the stat is at the same time sending the correct temp to the cloud yet displaying and controlling the hvac with a different incorrect temp.

That is good info. Can you please try deleting the two Remote Temp Sensors from the panel and leave them disconnected? Then reset and re-include the thermostat.

Do not add the RTS back for now, so there is no local network interaction between the RTS and Tstats. Do you notice the issue still?