I've got a Fres. K with around 11000hrs. Won't heat up all the way during heat disinfect. Trying to calib. the temp. sensors & the first two work fine. When I get to the 80 & 90 the pre-temp only register at 28.8. Is this my heater rod going or gone out?

Why don't you check your heater rod and find out...?

Ohm out your heater rod. Nine to thirteen ohms is considered normal.