Zen Thermostat - Random temperature increase / decrease

Hi all, I purchased a Zen Thermostat (Model ZEN-01 Zigbee version). These are the ones listed as compatible with ST. All in all working fine and doing the basics well.

The main reason for buying a smart thermostat was to hook it up to all my various open/close window sensors. If somethings open I have an automation to turn the HVAC system off. But I notice that on my thermostat and within the app that it drops the current pre-set “Heating Temperature” by 2 degrees.

Here is my automation. Simply checking if it’s “Heating” and just turning “Mode: off”

And here is the Thermostat History showing the Heating Temperature (Set-point) dropping 2 degrees.

I have another automation to detect when everything is closed, and if the condition is met it turns the Heating back on. This scenario generally self-corrects the temperature and returns to the old Heating Set-point (back up by 2 degrees). This scenario is just annoying more than anything else.

The random problem I’m mainly having is the temperature jumping up too high. I’m yet to pinpoint exactly when this happens (reliably), but it’s generally to do when my automation kicks in and turns the heater on. As mentioned above, it kind of corrects itself, but sometimes it feels like it jumps up to a “default” Heating set-point, rather than remembering the old-set-point.

Here is the history showing the Thermostat coming back on an jumping to 22.5 degrees (this seems to be this magic default set-point). For this particular instance, the set-point should have been at 21.5 degrees.

I’ve looked around a bit to see if i can at least set the default heating to another temperature, but to no avail. But my problem lies more around the randomness and the jumping of temperatures.

I don’t know if this is a Zen issue, a ST Thermostat device controller issue, or both? Happy to hear any thoughts or anyone that’s had similar issues and it’s a known bug?

FYI. Here is the device controller status from the IDE. There’s a lot of variables in here, and seems to be some double-ups.


[ “on”, “auto” ]

[ “off”, “heat”, “cool” ]

[ “off”, “heat”, “cool” ]

[ “on”, “auto” ]


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I have the Zen thermostat too because it supports my 4 wire system without the common power wire or need for any external power source since it uses the 4 AA batteries to power the unit.

This happens to me too, and I’ll bet your on to something that if we don’t set any temperature setting when changing the device mode, it will change the cooling/heating temperature settings to some default setting.

So to get mine too stop changing cooling or heating temperature to some default setting, whenever I set the Zen thermostat device mode to Cool, Heat, Fan, or Off, I also set both the cooling and heating temperature numbers to the exact same numbers every time. By doing this, I noticed that I no longer saw any setpoint entries in the device log whenever SmartThings change the Zen thermostat mode.

Also, since there are a lot of various Automation conditions when I want to change the thermostat mode, I setup four Scenes, one for each thermostat mode to use in my Automations, but each Scene that changes the thermostat mode sets both the heating and cooling temperature to the same numbers.

Thanks @DaWeav for your response. Good to hear I’m not the only one :wink: But, bummer if it seems to be a known issue. I may have to revert to your solution by hard setting the temperatures every time I change the mode. Eg. Heat = 22 degrees. I was hoping for it to remember the last preset so it would return to the temperature of choice.

I’m wondering if this a Zen related issue, or a ST device controller issue? Let’s see if anyone has any ideas? I’ll reach out to Zen also.

Might be a similar issue to what I’ve been experiencing.

I have scenes setup to change the temp from 17c to 21c in the morning , and also setup the same scene to set to Heat and Fan to Auto at 5:30 AM, as an example, with an automation to disarm STHM.
Occasionally, and gets worse over time, at 5:30 AM the change top 21c kicks off, then ~2 minutes later, the setting reverts back to 17C, yet STHM does disarm all the sensors and virtual switches I want it to.

The only advice from Zen was to perform a reset of the thermostat and reprogram the settings. Seems to last for about a year, then the issue starts to pop up again.

Just a thought. Love to hear if anyone has figured it out as my wife gets mad if the furnace doesn’t warm up the house before she gets out of bed!!!