Pentair Minimax NT temp reading

[minimax]

New to the forum - I have a minimax NT and this is my 3rd season for it. When the system is running, but heater is not on, the temp slowly climbs all the way until the window reads "HI". The water temp if anything, shoulf read "Low" because the water is freezing cold. Any idea what would caude the thermostat to give a bad reading like that? Ijust opened it Friday, and I'm thinking since the water isn't yet perfect that could impact the thermostat. Any ideas? Calling Pentair tomorrow when their service lines are open. Thanks in advance.....

[muss08]

Thermostat is probably bad