How a Controller Runs a Program

An irrigation controller stores one or more programs (start times, run durations, day schedules). On each scheduled start it steps through the active zones in sequence, closing the common circuit and pulsing 24 VAC to each zone output. Failure to execute a program can originate in the timer logic, the power supply, or the wiring between the controller and the field valves.

Common Symptoms

Scheduled programs do not activate any zones at the set start time
Display shows correct time and program but zones never fire
Manual zone test works but automatic programs do not
Controller display is blank or shows a low-battery / power warning
Some programs run; others are silently skipped

Diagnostic Steps

Confirm AC power. Measure voltage at the transformer output terminals inside the controller — should read 24–28 VAC. A reading below 20 VAC or 0 VAC indicates a blown fuse, a failed transformer, or a lost AC supply to the outlet. Replace the fuse or transformer as needed.
Check the backup battery. A dead or missing battery on controllers with battery-backed RAM causes all programs to reset to factory defaults after a power blip. Replace with a fresh 9 V (or the model-specific battery) and re-enter programs.
Verify the program is active. Navigate to the program settings: confirm the program is not set to Off or Skip, that at least one day-of-week (or interval) is selected, and that run times are greater than zero for each zone. Controllers with a seasonal adjustment knob can silently zero out all run times if set to 0 %.
Check the current date and time. If the controller clock drifted or reset (battery failure), the program triggers may never align with the real time. Re-set the clock to the correct time and day.
Test the common wire. With a multimeter set to continuity or resistance, measure from the C/COM terminal on the controller to the common wire splice at the first valve manifold. A reading above 5 Ω or an open circuit (OL) indicates a broken or corroded common wire — no zone can fire without a complete common circuit.
Test each zone output. With a zone active, measure VAC between the zone terminal and COM at the controller. Expected: 24–28 VAC. No output on a single zone points to a failed zone output on the controller board or a shorted solenoid on that zone (shorted solenoid can trip a controller's internal protection).
Check for a rain sensor or soil moisture sensor override. Many controllers have a sensor bypass switch. If the sensor is detecting rain or adequate soil moisture, the controller will skip programmed starts. Temporarily bypass the sensor (flip the bypass switch or disconnect sensor leads and jumper the sensor terminals) and attempt a manual program run.
Inspect the controller terminal strip. Look for corroded, loose, or reversed wire connections. The common wire and each zone wire should be firmly seated in their terminals with no bare copper exposed beyond the terminal clamp.

Root-Cause Summary

Timer / program fault — program disabled, wrong day selection, run times at zero, or seasonal adjustment set to 0 %
Clock reset — battery failure wiped programs or clock; programs never trigger at the correct time
Power fault — blown fuse, failed transformer, tripped GFCI outlet, or dead backup battery
Common wire break — open circuit on the C/COM wire prevents all zones from completing the 24 VAC circuit
Rain or soil sensor override — sensor holdoff is preventing scheduled starts
Controller output failure — individual zone output or entire controller board has failed