Question
QUESTION: We have a Irritrol Systems HR-6100 controller and it has been working fine for years until now.  It was setup with two zones that work including A for the lawn and C for citrus trees and bushes.  C isn't working currently but the A zone is working.  What would be the common issues for this problem?

ANSWER: Hi
A and C refers to programs each program can have up to 6 zones. When you say zone C is not working do you mean all the zones on that program. If a program don't have start time it will noy work.
If you clarify you question a little bit it will help me to help you.
Regards
Guillermo

---------- FOLLOW-UP ----------

QUESTION: To clarify my problem, Prog C is Zone 4 only (citrus trees).  This zone/prog is not working.  Prog A (Zones 1-3,5 sprinklers and drips) works fine.   Is it possible that the water is shut off for zone 4 only?

Answer
Hi the problem is the valve does not open, this is caused by:
1)The timer port is not sending 24V to the valve, turn on that zone an measure the AC at the port, one lead at the port and the other at the COM port. If you have 24V or so,
2)The wire to the valve selenoid is broken or disconnected, check it,
3)The selenoid is damaged on does not open, replace it or
4) The valve is stuck, open it and clean. Or last
5) Replace the valve.