Light comes on says tank is full. But it won't start

The full light normally comes on when the tank is full. Emptying the tank and re-installing the tank should allow the system to reset. However, if the tank isn't pushed in all the way... the full switch and indicator light will be fooled into reporting a full condition. My suggestion is, first pull out the tank, look at the float and the tank full switch. Become familiar with these two items and confident that 1) the float is not stuck in the up position; 2) the tank full switch that the float is supposed to actuate will toggle (press your finger against it and let it return.) After this exercise make sure the tank is seated all the way in place. If your issue is mechanical, its easier to fix than if it's electrical, and if it is electronic... (just pray that it isn't).

Sounds like your float is stuck in the full position, or the sensor that shows full is stuck on full.
If tank is empty but shows full, problem lies where full signal is coming from.

empty the tank, and clean the dust off of the condenser in the front or clean the filter. if it still won't turn on, may have a bad sensor or a siezed compressor.

Check the over fill switch in the tank. If this is stuck it thinks the tank is full and won't come on. After that your compressor may be bad or the starter for the compressor. The Dehumidifier is basically a small air conditioner that condenses moisture in the air then it drains into the tank.

Hi and welcome to FixYa, I am Kelly
Most likely the sensor assy has failed. See section 6 of this link:
http://www.appliancepartspros.com/partsearch/model.aspx?model_id=5520042&diagram_id=28700153#d28700153

Detailed View: ($18.04)
http://www.appliancepartspros.com/part_details.aspx?part_id=4652359

This senses water and humidity levels.
Thanks for choosing FixYa,
Kelly

Try resetting the bucket, making sure that it is set properly and triggers the safety lever/switch. If that doesn't solve the problem. Turn the Master ON/OFF Switch to OFF, unplug the unit from the wall outlet and wait 12-15 minutes. Plug the unit back in and turn the Master ON/OFF Switch to ON. If the bucket is installed properly, the unit should revert back to the original factory settings.

Hope this helps solve the problem.

Dont spend to much time trying to repair dehumidifier they are very cheap to replace. Most dehumidifiers have lots of problems because they are made so cheap. Just replace the dehumidifier you will tank me in the end.

If the unit is titled forward at all, the "full bucket" "trip switch" will not trigger off as it should. Be sure the unit is on a flat, level surface, or leaning backward slightly--this also aids drainage through the drain tube, if that's your set-up.

I thnk your tank is askew. Adjust the osition of the tank until the light goes off ...

Most dehumidifiers rely on a float sitting in the pail to rise, turning off the switch. Check and see if the float moves clean and smooth, and is sitting in the pail rather than resting on it's brim.

There may be other safety switches, like a temperature sensor to turn it off if it runs the risk of freezing up or overheating.