remove power. separate your solenoid from everything between it and the tank. your shetup should look like:
tank, reg, solenoid, nothing.
apply and remove power several times.
Reassemble setup, see if it is fixed
if not,
remove power
get screwdriver (see note below)
disassemble solenoid (note: disclaimer i am not liable for anything that happens, use at your own risk

)
clean with compressed air (see note above)
oil/grease parts that might need it (see note above)
reassemble (see note above)
test (see note above, again)
enjoy!