Hi, the problem got solved long time ago but I forgot to post an update here. The reason was that the old thermostat was not working ever as the cables in the boiler were not connected.
The specialist came; sorted out the cables in the boiler and the old thermostat was working perfectly. Then I installed the new google nest thermostat easily - as I got great instructions here in this forum. many thanks!!!!!! thermostat works great and I love it
The specialist came; sorted out the cables in the boiler and the old thermostat was working perfectly. Then I installed the new google nest thermostat easily - as I got great instructions here in this forum. many thanks!!!!!! thermostat works great and I love it