KMN

There was an older post concerning a Sundance model 850 spa running and showing ICE even though the water temp was 102. I replaced the temp sensor (in the filter compartment) a while back based on other error codes and everything has been working for a while. It seems the last couple of times it got cold out (20 deg F) I am having the ICE problem where the hot tub thinks there is a freezing condition when there is not and runs continuously. I have reset the breaker which did not work. My question is if it is a sensor problem what sensor is responsible for thinking there is an ICE condition? Is it the temp sensor (that I replaced) or the other sensor in the heater or somewhere else?