Donexon Varmo TZ problems

[Peter C 0]

Does anyone have any experience with the Donexon Varmo TZ Pro thermostatic radiator head?

And if so, have you managed to solve the problems that come with this head?

This head has with 2 temperature sensors. The installation template gives you the possibility to give both sensors an offset so they give both more or less the same reading and are more or less equal to the real temperature.

The last time I did this for one of my heads is now less then 24 hours ago. At this moment one sensor indicates that it is 21.6 °C, the other one claims it is 30.2 °C, while in reality it is just 19 °C. But it is also possible that within an hour both sensor give very different readings.

When the room cools down, the first sensor that passes the heating setpoint opens the valve a bit. When the second sensor passes the heating setpoint the valve is fully opened.

Actualy, these thermostatic radiator heads are not usable to control a room temperature because of the unstable temperature sensors. I could buy some new and better ones, but they don’t come cheap.

An other solution could be to not use the thermostatic part of the heads. Just use it to open and close the valve remotely. I could buy an external temperature sensor for each temperature zone and use this temperature together with the climate panel, which I can read with LUA, to decide whether or not the valve should be opened. To open or close the valve I could send 5 °C or 27 °C to the head as heating setpoint, making sure the valve is fully opened or closed.

To prevent the climate panel to overwrite the heating setpoint through the association with the thermostatic head, I will have to replace this association by associating the climate zone with a quick app (Add Device – Other). This quick app doesn’t have to do anything. It is just needed for creating a climate zone.

In theory this should work. Any suggestions will be welcome.