Mesa Nomad 100 Head Reverb / Footswitch Problem - very odd..

[Acid Test]

I have a Nomad 100 Head that was bought used. I can't get the reverb to work when the 6-button footswitch is used. The footswitch reverb light can be switched on and off but no reverb sound. Unhook the footswitch and the reverb works fine. I tested the cable and it is fine. This puts the problem with the head or the footswitch ($139). Any idea where to go from here? Did I miss something obvious?

thanks in advance for your help

 

[Acid Test]

The issue was entirely in the footswitch. Replacing it fixed the problem.