I have a 4-year old Kenmore 65-pint dehumidifer which sits in a basement room containing electronics, etc. and I keep the relative humidity below50%. It has functioned well until I turned it on for this summer season (in the winter, hot air from the furnace keeps the room dry as a bone). Nothing has changed in the room, or the basement, which would affect the ease with which humidity could leak back into the room.
I keep a digital thermometer/hygrometer in the room (double-checked for accuracy with another unit elsewhere in the house). The problem seems to be the (digital) humidistat (which has a range of 40 - 60%) which now seems to be about 10 - 15% too high. As a result, even with the dehumidifer set at 40%, the steady-state humidity in the room barely goes below 50%.
I checked the warranty and it only applies to the sealed components (condenser, compressor, etc) so I opened the unit and found no evidence of a humidistat adjustment or trimmer. The humidity sensor is mounted on the inner frame of the unit, within the stream of air flow between back to front, next to the sides of the coils. When it has stopped running at an ambient humidity of 50% (even though set to 40%) it restarts again when I blow moist air from my mouth at the sensor.
It looks to be sourced from LG, and browsing in stores I see newer units which allow set points down to 30% relative humidity, as well as low temperature operation. I'm toying with the idea of simply replacing the unit, but wonder if it's worth the expense of having a non-warranty failure repaired - or the hassle of ordering a replacement sensor and trying it myself.