H can indicate cooling with the lid held closed after pausing or interrupting drying on documented AQUA models. Wait for that protection to finish before trying to open it.
The AQUA Japanese FAQ describes this state on machines with drying. This explanation does not define every code that starts with H.
Check what happened before the message
If you had just paused drying or turned the power off and back on during that function, heat may remain inside. The H text and the lock indicator then accompany the model's expected release wait.
Do not pull on the lid, insert tools into the latch, or restart heating to try to clear the warning. Cutting the power does not immediately remove the internal temperature either.
Check the manual for the cooling behavior and wait for the indicated release. If it does not end according to that instruction or the message includes additional characters, keep the full sequence and request support. Child UL and open-lid U4 are interpreted separately.
Record the full message and whether it appeared after drying; this helps distinguish this thermal hold from another H alarm.