U15 refers to drainage during drying in the documented Panasonic FR1 washer-dryer. It is a different issue from U11, the general drain error during washing use.
The Panasonic FR1 reference includes the NA-S106FR1 washer-dryer and limits this alert to its drying function. Do not apply it to a standalone dryer or a washer without drying.
Check which transition it appears during
Note whether washing had finished and how far the drying cycle had progressed. Do not rerun only a hot cycle to reproduce the message.
When the unit has stopped and cooled, inspect the external drain path and any recent installation changes. The hose position must match its manual, without adopting measurements from another setup.
Do not open the internal circuit or try to release the door with water or retained heat. If U15 appears again after the permitted external checks, request inspection of the drainage for that function. A proper wash does not prove it can complete drying.
Report U15 together with the drying phase and the combo model reference; avoid summarizing it as an indistinct washing failure.