I bought a second hand Nest Thermostat v1 (the European model with heatlink). I installed it and the Thermostat seems to work. The central heating boiler (Vaillant hrPRO CW3 VHR NL CW 3/3) seems to turn on but not off.
Even though it's in Dutch, this is the official manual of the boiler system. Maybe the schemes give some more insights to some people.
After that I removed the old thermostat and connected the wires (t1/t2) on the heatlink to the Nest thermostat.
At first I used a cable between the heatlink and boiler that might have been not thick enough (phone cable) then the boiler showed a Vaillant F49 fault. But after I disabled everything again, used a thicker cable, and did a reset of the boiler, heatlink and Nest the error was gone.
Now it seems that when I enable the three devices. I can enable the boiler by turning the heat up on the Nest thermostat but it won't stop heating anymore when I turn the temperature down on the thermostat.
Did I connect something wrong? Or do I still have to change some wires in the boiler in order to get this to work properly?
Also, what is the red wire between 3/4 doing in my boiler? Can I remove it? Was it necessary for the old thermostat to work?
Or, do I need to connect the Heatlink and boiler with 7,8 or 9 instead of the "bus +/-"? The manual seems to show something about a manual mode.