I have a Hayward pool heat pump, model HP 2100, that is about 8 years old. Earlier this year, it worked for about a week, then stopped working and displayed a "Sensor Failure" code. I was busy and on the road for work so I left it alone for about three weeks. I finally found the repair number but before calling I tried it one more time and it worked. Go figure.
So it's been working for about a week now. Last night I was doing yard work and went over to it to cool off from the cold air that blows out the top of the unit. To my surprise, the fan is now running in reverse and sucking in air from the top! It is still heating the pool.