Diagnose in order, not by instinct
When automatic irrigation fails, the urge is to take it apart. Almost always it’s the other way round: 80 % of the faults are in three places and can be checked in five minutes. The right order goes from the cheapest and most visible thing to what needs dismantling.
- Is there water at the inlet? Main shut-off valve open, pressure, empty tank.
- Does power reach the controller or the solenoid? Voltage at the coil.
- Is the controller hiding a fault? Dead batteries, a dirty jumper, the display.
- Does the valve open? You hear the click or you don’t.
- Does water come out of the valve? And at what flow rate.
- Does water reach the zone? Clogged emitters, a pinched line, the filter.
- Does it come out of the drainage? A badly drained pot or saturated substrate.
Each step rules out a whole group of causes. If you jump to step seven because “it’s bound to be the valve”, you replace a €40 part and the problem is still there.
Symptom 1: it doesn’t irrigate at all
| Likely cause | How to check it | Fix |
|---|---|---|
| Main shut-off valve closed | Open it and test | Open it |
| Controller has no batteries | Replace them and set up again | New batteries |
| No voltage at the coil | Measure at the connector, controller ON | Check the wiring |
| Burnt coil | Measure resistance: very high = open | Replace the solenoid |
| Obturator blocked by limescale | Dismantle and clean | Clean it, check scale |
The most underestimated case is the burnt solenoid: it lasts for months and then one day it stops opening. If the voltage arrives and there’s no click, that’s the most likely culprit.
Symptom 2: it irrigates, but very little
Here the cause is almost always physical, and there are three main candidates:
- Not enough pressure. A raised tank with little height, or a line that’s too long, gives weak emitters. The solution is the tank height or a pressure regulator.
- Partially clogged filter. Flow drops progressively: it’s the classic symptom. Clean the filter every season.
- Emitters clogged by limescale or algae. If the flow is irregular from emitter to emitter, the problem is in the emitters.
Check the flow with a cup and a stopwatch: measure for one minute and compare with what the emitter’s datasheet says. Flow figures are in the drip line installation.
Symptom 3: it irrigates too much
This is the most serious one, because it kills plants. Usual causes:
- Controller in continuous mode because of a dirty jumper or a stuck button.
- Recirculation drain pump: if the pump’s return flow isn’t right, the valve stays half open and drips.
- Tank that overflows as it fills. The fill line needs a non-return valve or a level float, and a faulty float fills it right to the brim.
- Clock out of sync: an hour jump can trigger schedules you didn’t expect.
If the system overwaters now and then, look first at the history on the dashboard: the exact time and duration of the cycle often give away a badly configured controller.
Symptom 4: it irrigates zones it shouldn’t
If the solenoid stays open after the cycle ends, it’s almost always one of these two:
- Limescale or grit in the obturator seat.
- Low quality solenoid: a thin coil degrades with use.
Also check whether two solenoids share a line: if the wiring is wrong, closing one opens the other. It’s a classic wiring fault.
Pressure: the silent cause
Mains pressure varies through the day and depends on other users. A system correctly set at 8 in the morning can drip at 8 in the evening. The solution is a pressure regulator at the end of the line, not adjusting the controller to compensate: if you increase the run time because pressure drops, at the moment of highest pressure you’ll overshoot.
Typical working figures for drip are between 1 and 3 bar, and higher for sprinklers. Confirm the values in your equipment’s datasheet, which is where the specific flow and connection data are.
The filter: the maintenance that prevents everything
- A filter on the inlet of each zone, not just one general one.
- Cleaning at least once per season, before the hottest part of the year.
- Flushing the lines at the end of the irrigation cycle.
- If your water comes from a well or a tank, check limescale build-up: it’s the most underestimated cause of low flow.
Checklist before you touch anything
- Note whether the fault is constant or depends on the day and the time.
- Check the history if there’s a dashboard; if there isn’t, write the times down by hand for a week.
- Check water, power, batteries and obturator, in that order.
- Measure the real flow of one emitter, in a cup and with a stopwatch.
- Check the filter and the line pressure.
- Replace the solenoid only after ruling out the four before it.
If the fault is still there and it’s already in the coil, then yes: replacing the solenoid is the solution.
Sources and next step
The pressure and flow spec for your specific equipment is in the manufacturer’s datasheet; for the hard water part, hard water and limescale. To avoid it in future, the drip irrigation installation guide.
External sources
- Rain Bird: sprinkler system installation guide (PDF) — flow per zone, filtration and line sizing in an irrigation installation.