I'm just guessing that it's the valve.
Your heater hose is connected to a valve that is mounted sticking out of the firewall. There's a cable that goes from the knob that you twist on the dash through the firewall to that valve.
I'll bet that valve is stuck from crud/deposits in your coolant. Try to move the end where the cable attaches with your hand, or a pair of pliers. Once you get that valve unstuck, the knob on the dash will work again.
And I'll bet you'll get some hot air blowing, too.
Flunky