According to the instruction manual this type of dehumidifier works by chilling the water out of the air and then heating the air back to room temperature before sending it back to the room.
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How cold is the air that is coming out?
Page 11 of that manual says that it is normal for it to be blowing out
warm air.
It also says in there that you should leave it on rather than switching it on and off, it will switch on/off automatically as it is needed.
But don't forget the water collection tank will need emptying occasionally, it should beep to let you know when.
If the air coming out is much below room temperature then it would suggest that the re-heating is not working and the unit may be faulty.
Although remember if the air going in is very cold it will also be cool coming out again. (The reheating will only warm it up by so many degrees, its a dehumidifier not a heater).
If you still think that it is not reheating at all then take/send it back for a replacement?