When using a volume pedal with the ES-8, you must not only plug it in to the ES-8's Send Vol/Return Vol jacks, you must also activate it in the Loop On/Off screen.
As there is not a dedicated switch on the ES-8 for the Volume Loop, this is how you would turn it on or off:
Activate Volume Loop
1. Press DISPLAY/EXIT to get to the Loop On/Off screen.
2. Press Right Arrow until cursor is under the "V".
3. Press +.
4. Press Write three times to save configuration.
De-activate Volume Loop
1. Press DISPLAY/EXIT to get to the Loop On/Off screen.
2. Press Right Arrow until cursor is under the "V".
3. Press -.
4. Press Write three times to save configuration.