I have a Hayward H400IDL2 pool heater that has an error code of SF. I believe this is a bad temperature sensor. From what I have been able to figure out, there are 2 of these sensors, 1 for high temp & 1 for low temp. How can I figure out which one is bad? Is there some type of test to them that can be done, ex: resistance, voltage while running, etc. I have some electronics & electrical experience & have a DVM to check circuit problems. Thanks.