hotpoint RFB50P f/f

Hi, this fridge/freezer appears to be working fine, the temp dial is set to 3 and both sections get to the correct temperature. but the high temp light comes on randomly?
i found a single post elsewhere (not very clear tbh) and the person mentioned that you need to replace the green sensor? but all i can find on qualtex is the normal thermostat and an alarm thermostat, is it the latter? and where is it housed?
as always, any help is most appreciated.

David