Hard to know without having it in front of me, but a few things to try:

1) The pedal has a calibration knob (maybe called Minimum Volume) – try adjusting this and see if it makes a difference.

2) The H9 has various settings related to pedals. Try setting EXPTIP to PEDAL.

3) Try the pedal calibration (PDLCAL = ON)

4) Try wiggling the jack in and out in case the contacts are dirty.

Quite likely that one of the above will produce a result …