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Faulty heatlink?

I wanted to change my nest connectivity from on/off to opentherm (my burner accepts opentherm). Connected all the wires correctly, but got H73; no opentherm found. Now, even when I unplug the power supply of the heatlink, but leave OT1 and OT2 connected, the burner keeps heating. Only when I unplug OT1/OT2, the burner stops. This, to me, shows that there is some kind of direct contact between OT1 and OT2. I tried another heatlink, which works directly. Does anyone know if I can solve this on the heatlink's main board or is my heatlink just fried..?


3rd Gen.


Already did multiple fact resets of both thermostat and heatlink