It has always stayed on since I put it in use. During building and testing it the LED on the board didn't light up.
does the #10 led light up when testing that channel, or not at all? this is curious ... either bad LED or installed backward or shorted across?
with no power connected to board, I would do the following as troubleshooting steps
a) look closely at the gate to terminal and terminal to terminal pins on the triac and make sure they are isolated
b) look closely at the 120V side of the opto coupler socket ... make sure those pins are isolated and you are not bypassing the opto altogether
c) check pin 18 on the PIC, if it is being grounded somehow it is turning the opto on and in turn activating the triac gate
d) check continuity from pin 18 on PIC (not socket) all the way to - (neg) side of #10 LED, and then across the LED all the way to pin 2 (cathode) of opto