I got finally installed my HEATIT ZTRM2fx thermostats that I bought a couple of years ago to replace the old mechanical thermostats. Unfortunately, it turned out that two of the thermostat locations do not have a setup for a floor sensor - and since ZTRM2fx does not have internal temperature sensor, the only option is an external temperature sensor.
I have thermometers in the relevant rooms, connected to openHAB, but not z-wave. Is it possible to use those to “simulate” an external sensor?
(I asked Chat-GPT and it very confidently recommended to create a rule that fires on update of the thermometer and then sends command with the value to the item associated with the “External sensor” channel of the thermostat. It works in the sense that the rule triggers and the value is sent, but the thermostat does not accept it and still shows “Error 5”, meaning error in the external sensor.)
I also tried to send the temperature to the related item as a command manually, in all possible formats, but it just gets ignored.
And if this cannot work, can someone recommend a preferably cheap external sensor?
Alternatively, I have seen some old topics that, if I understand them correctly, suggest connecting a wired sensor but let it measure air temperature, instead of floor?
This seems not to be a problem of the temp. Sensor, as they all give you only a temperature. You may check what kind of data the thermostat requires. I use danfoss devices and they accept „2150“ as a temperature of „21.5°C
Thanks for the suggestion, but it does not work. I tried sending temperature as is and multiplied by 10 or 100, both as number, string, ans Quantity, but the result is always the same: the item auto-updates to “0 °C” after a couple of seconds, and the thermostat still shows “Er5”, which means error with the external temperature sensor.
Note: Do I need to connect the thermostat’s association group “External temperatur” to “Controller”, for this to work? The problem is that I have tried that, but the change remained at “pending” state…
According to the manual, an external sensor MUST be connected
When you have decided on the sensor mode you want to use, press the Center (confirm) button. If you choose F without having a floor sensor connected, Er4 will be shown in the display. If you choose A2 or A2F and there is no external sensor installed, Er5 will be displayed on the screen.
I have somehow assumed that external means z-wave, this being a z-wave device. But now I have found that they sell an external sensor, which connects by a wire, so I am afraid this may be the only option. (I sent them a question about this.)
Otherwise, I found that I can still control the on/off state of the thermostat from openHAB, so it works in a sense - but the display shows “Er5” at full light intensity, which is annoying. (Apparently, the dimming option is ignored when there is an error.)
So, the realistic options are either buying the external sensor or buying another thermostat (probably zigbee). In any case it means paying for an electrician….
The external sensor is just a wire with a thermistor at the end, in the US it’s not more than $10
Installing the thermistor is very simple if you want to control the air (room) temperature, it’s impossible if you want to control the floor temperature as the thermistor must be embedded in the floor.
I have just installed a zigbee thermostat and it is really very simple, again in the US, cut power to the thermostat from the breaker, disconnect 4 wires, the line and neutral coming into the thermostat and the line and neutral going to the floor heating and of course the sensor. That is it.
