I believe these models have a thermal switch on or near the heating element that normally runs the fan until the element has cooled. Similar to your home furnace. If the fan never shuts off this switch is likely bad. IF it takes a long time to shut off then it may be out of calibration. In either case they are non repairable parts and have to be replaced. If the heater is in a high spot resulting in a high ambient temperature it may take a while for the fan to shut down.
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I believe these models have a thermal switch on or near the heating element that normally runs the fan until the element has cooled. Similar to your home furnace. If the fan never shuts off this switch is likely bad. IF it takes a long time to shut off then it may be out of calibration. In either case they are non repairable parts and have to be replaced. If the heater is in a high spot resulting in a high ambient temperature it may take a while for the fan to shut down.