When I'm looking on the installation from Bobby it seems that both cabe coming from the Heater platine together connected to the brown cable?

I'm trying to connect my new Tada wireless smart Thermostat to the Heater system and replaced my old Nest 3.
I have connected the
Black in the COM and the
Orange in the NC
each to the both coming from the heater Platine.
Whats happening now is that the Isotwin heating the water to 77 degrees than the Gas is cutting but the Isotwin is running. If the temperature from the water goes down Gas coming back and heating to 77 degrees.
When the extended kit stop to heating (light of)
The Isotwin stay running and heat the Water.