Why is water leaking from the steam wand?

Water is leaking from the steam wand whenever the machine is on regardless of the mode the machine is in. There will be a stream of water out of the wand even if the machine is just in the "heat water" mode. I suspect the steam control knob is faulty because it doesn't turn smoothly, but I'm not sure how to confirm this. The knob is in the closed position. I have recently descaled the machine. Is there a way to confirm that the knob is the issue? Is there anything else I should check? The frother? If it is the knob, I've seen that I can order a replacement, but I'm not sure how to remove it from the core.