alan50, arrange things so that you can be near the valve with your ear near to the solenoid when the current is switched on. You should hear a 'click' followed by the buzz or vibration. The click indicates that the plunger inside the solenoid has been pulled upwards to open a port which does the same thing as the manual bleed screw. I suspect that the plunger is stuck in the solenoid. If that is true you can unscrew the solenoid and free it up. If it is too rusted out or something, you can easily replace it. Shut off the water first so that you can keep from losing the O-ring seal.

Purchase a valve kit at a place like the Do-It-Center ($6.99) and take the valve apart and soak it in something that will remove the scale build up. You can ruin the housing if you clean out the holes any other way. Then install the parts (valve bladder, o-rings, washers). The valve will work if you get it back together correctly. It make take up to 5 cycles for the bladder to take the proper shape for the value to work with the electronics. Just use the bleed valve to assist the unit. It will keep itself open with the electronics on.