Hello, thanks for contacting us. My name is XXXXX XXXXX X'XX try to assist you with your issue.

Is The model HG-425e?

What do you mean by "not sustaining"? What happens if you keep pressing the keys on the keyboard? Does the note sustain that way?

The contact on the pedal might not be working or may need cleaning, are you up to do a self repair?

Best.

The Sustain pedal, as in most pianos, makes the keyboard work as if you were not releasing any keys after pressing them.

That is why I'm asking what happens if you keep your keys pressed, do you hear the notes ringing as they should?
And when you release those notes do they turn off?

What happens if you press the pedal and hit a note hard and release it quickly? how long does the note stay ringing/resonating?

I'm trying to figure out if it is the pedal or it is just that you don't hear the difference between sustain and not sustain which may probably have to do with a bad piano sampler which could need replacement.

Best.

I don't feel bad, I'm trying to diagnose your issue from the hints you are writing and not by hearing the actual piano itself, it is not an easy task...
:)

Anyway, if I have to guess from what you are describing, 4 seconds is *not* very bad, depending on what note you are hitting... You may not have any problems, you may just dislike your piano sound and that is a definite possibility,

Lets try the following test please:

Get a watch, clock or stopwatch with a seconds indicator.
Hit the C1 note use that note and only that note, it must be a low keyboard note) as hard as you can and leave it down, pressed, without releasing it (do not use the pedal just yet).
Please take note of the length of the sound using the stopwatch from the initial key press until you cannot hear anymore. Approximate values in the range of seconds are OK.

Now release the key, press down on the pedal firmly, and hit the note again as hard as you can and release it quickly keeping the pedal firmly pressed down.
Take note of the length of the sound.

Please post back with your results. With this information I will surely be able to diagnose this.

Best.