Question
My controller seems to have stopped responding, i.e., it shows that it is programed however none of the stations are coming on.  I tried the manual button, but nothing happens.  It is a 12 station unit with 10 in use.  Probably about 11 - 12 years old. I assume the problem may be internal.

Answer
Hi John

I know it sounds elemental, but ensure the water to the system is on.  If it is read on...

Valves typically require voltage minimums to operate.  The first thing to troubleshoot in this case is the controller.  Ensure that there is 24 V being supplied by the controller to the valves.  Where the valve wires connect to the terminal strip on the controller, use a volt meter to monitor the line voltage when the zones are supposed to be on.  Put the black probe on the Common terminal and the red one on a zone terminal after you manually turn on the zone from the controller.  It should read between 24VAC and 27VAC.

If the voltage does not vary beyond the range noted above, you may want to ring out the wires and check the continuity from the controller to the valve(s).  Set the multimeter to the ohm setting. The symbol for ohm is the Greek letter omega. If there is more than one ohm setting, choose X1.  A digital meter performs the test providing a numeric reading.  

Note that while the probes are not touching anything, the multimeter will indicate a reading of infinity. A reading of infinity means that the circuit is open. When you touch the two probes together, the reading changes to zero. A reading of zero indicates that the circuit is closed or complete. A complete circuit is one that can conduct electricity; an open circuit cannot.  Place the black probe on the common wire and the red one on the suspect valve wire.  Check the resistance of the problem circuit. If the system has valves that typically measure about 30 ohms of resistance, and the one in question measures 6 to 8 ohms, suspect a short circuit. To verify this, go to the valve box and disconnect the field wires from the valve. Check the resistance directly at the valve. Confirm whether the short is in the solenoid. If so, replace the solenoid. If not, it's time to look closer at the field wiring.  

Return to the controller and check the resistance through the circuit. With the solenoid removed from the loop, the resistance reading through only the field wiring is probably just a couple of ohms. If the resistance measures more than this, the issue lies in the wiring, not the solenoid.

Good Luck
Tony