We only used this dehumidifier for a few month when the error occured. I couldn’t find anything reliable in the manual or on Trotec website.
I was not entirely sure if the error was L1/F1 or LI/FI, so I searched for both, not to much luck to begin with.
Browsing on Amazon, I saw this Q/A with very similar error.
The device was unplugged for 2 days, so I took off the front cover, removed the filter, cleaned the fins under it with a soft brush, up and down direction. Careful!!!!! Super sensitives! Put the filter back, cover back and plugged it in.
Magically it works!!!