Hmm I thought maybe the temp sensor burned out, it seems it's a PTC at 1.5R at room-temp. Then I thought maybe the schematic was labeled wrong, but no I had the 3pin connectors for the fan VR swapped with the PTC sensor. That makes sense in the op-amp circuit with the MCU setting P0.1
I think I the triac burned out ages ago, because I definitely remember it working, then stopping working in the middle of something. Then ages later I replaced it, and a filter cap too close to it's voltage rating. But I mixed up the connectors, and forgot all about it.