SP 33 sustain (middle) pedal intermitently fails

[Newbie17]

I own a PX560M keyboard with the wooden stand and an SP33 pedal board. I've had it for two years, but I have never actually used the sustain (middle) pedal till today. I tried it when I assembled it 2 years ago, and it seemd to work fine. Today I tried to use it to play Gymnopédie N. 1, and I found it works randomly. I tested it thoroughly and I am clueless. Might it be a firmware / configuration issue? The other two pedals work flawlessly, and this one was almost never used. Has any of you experienced the same issue?. Thanks.

[Brad Saucier]

Try pressing the pedal a good number of times.  This might help it start working if it's simply dirt from lack of use.  

[Mike Martin]

The middle pedal is a sostenuto pedal.  It sustains only those notes that are being held down when the pedal is depressed.  Are you certain it is not working properly? 

[Newbie17]

7 hours ago, Mike Martin said:

The middle pedal is a sostenuto pedal.  It sustains only those notes that are being held down when the pedal is depressed.  Are you certain it is not working properly? 

Yes, Mike, I know how it is supposed to work, that's why I mentioned I have never used in a few years, but now I need it to play Satie's Gymnopédie No. 1.

 

8 hours ago, Brad Saucier said:

Try pressing the pedal a good number of times.  This might help it start working if it's simply dirt from lack of use.  

Brad, apparently the problem is mechanical. I don't know if it is designed that way, but I have to step on the pedal really hard (to the metal) for it to work. So hard I feared it might break, so I added a piece of cardboard under the pedal board for extra support. It requires really much more pressure than the other 2 pedals. Is it that way by design or my unit might be damaged?