Eurotronic Spirit Thermostats firmware issues

Just got couple of these and main issue for me is that when I set them to Off sometimes it’ll not close the valve and radiator is still heating. I found that if I set it to 28C and then off (sometimes I need to repeat On/Off cycle) it will eventually shut the radiator completly. I’m considering sending them back to Amazon if I’m not going to be able to remedy this issue.