When a solar submersible pump misbehaves, the instinct is to blame the pump or the inverter. In practice, most field problems live somewhere else: in the well, the array, the pipework or the sensors. This guide works through the three classic symptoms, low flow, no water and short cycling, in the order you should check them. It deliberately stays on the water side of the system. If your inverter is showing a fault code or a dry-run protection message, start with our guide to solar pump inverter fault codes and dry-run protection instead, then come back here if the code side is clean.
First principle: the inverter is usually the messenger
A pump inverter measures current, voltage and runtime, and it reacts when the hydraulic side goes wrong. Low current can mean the pump is sucking air. Repeated dry-run trips mean the well is not recovering. Before condemning any electronics, answer three questions: Is there water at the pump intake? Is the array delivering full power right now? Is the path from pump to tank open and leak-free? Most diagnoses end at one of those three.
Symptom 1: Low flow
Well drawdown. The most common cause overall. The static water level may be fine, but once pumping starts the level around the borehole falls (drawdown), and if it falls close to the intake the pump delivers less and starts to gulp air. Flow that starts strong and fades after twenty minutes is the classic signature. The fix is hydraulic: lower the pump if the borehole allows, reduce the duty point, or accept a lower rate matched to what the well can sustain, as covered in our deep well solar pump inverter guide.
Not enough array power. Dust, new shading from grown vegetation, a failed module or a string fault all cut the power the inverter can draw on, and a solar pump shows lost power directly as lost flow, especially in the morning and afternoon. Compare midday performance with the system’s history before assuming the pump has worn.
Intake screen or impeller problems. A clogged intake screen starves the pump; worn impellers from sandy water pass less water at the same speed and draw slightly less current doing it. Both need the pump pulled, which is why they are checked after the surface causes, not before.
Leaks and restrictions. A leaking rising main or a partially closed valve sends water everywhere except the tank. Watch the pressure behaviour and walk the line. On long cable runs, voltage drop can also leave the motor short of power at full load; cable sizing matters more the deeper the pump sits.
Symptom 2: No water at all
The protection is doing its job. If the inverter reports dry-run or low-load, believe it until proven otherwise: the well level has likely fallen below the intake or the level sensor is correctly reporting a dry borehole. IDEEI pump inverters such as the LX200 solar pump inverter include pump-oriented dry-run protection precisely so this condition stops the pump instead of burning it out. Wait for recovery and check levels before resetting repeatedly.
Check valve stuck or failed. A stuck non-return valve can hold the column so the pump works against a closed door, or let the column drain back so every start begins from empty. Either way the pump sounds busy and delivers nothing.
Air lock or a broken rising main. After any work on the system, air in the line can stop delivery until it clears. A cracked pipe below ground shows as a pump that runs, a wet patch or a borehole that mysteriously never fills the tank.
Pump set above the water. Seasonal water tables fall. A pump that was safely submerged at installation can be left high and dry by late dry season; the permanent fix is a deeper set or a managed pumping rate, not repeated restarts.
Symptom 3: Short cycling
Short cycling means the pump starts and stops far more often than it should, which wears contactors, sensors and the pump itself. The usual causes are control-side, not pump-side:
- No tank, or a tank that is too small. Without storage, every small demand starts the pump. A correctly sized tank turns dozens of starts into a few long, healthy runs.
- Level sensor placement. Tank float or level sensors set too close together start and stop the pump on ripples. Widen the gap between stop and start levels.
- Fast-moving cloud. On broken-cloud days the array power swings and a system without level control hysteresis can chase it. Proper sensor control with sensible delays rides through passing clouds instead of cycling with them.
- A leaking tank outlet or trough valve that keeps calling for water in small sips all day.
Symptom, cause and check at a glance
| Symptom | Likely cause | First check |
|---|---|---|
| Flow fades after 20-30 minutes | Well drawdown | Dynamic water level vs intake depth |
| Flow low all day, worse at edges of day | Array under-delivering (dust, shade, module) | Clean array, inspect strings at midday |
| Flow low, current slightly low | Worn impellers or clogged intake | Pull pump and inspect wet end |
| No water, dry-run message | Well level below intake | Rest level, wait for recovery, retest |
| No water, pump sounds loaded | Stuck check valve or blockage | Valve and rising main inspection |
| Starts and stops every few minutes | Sensor gap too tight or no storage | Level sensor positions, tank size |
When it really is the inverter
Work the water side first, but do not ignore clear electrical evidence: fault codes that return immediately on a verified-good pump and cable, output that is missing a phase, or a drive that will not start in full sun with a full well. Those are drive or wiring faults, and the fault-code guide linked at the top of this article walks through reading them. Describe the symptom pattern, not just the code, when you ask for support: when it happens, what the well and weather were doing, and what you have already checked. That pattern is what gets a system diagnosed in one exchange instead of five.
Frequently asked questions
Why does my pump work in the morning but stop by afternoon?
Usually drawdown plus heat: the well level falls through the pumping day while array temperature rises and output dips, and the two together push the system below its working point. Check the dynamic level in the afternoon, not the morning rest level, before changing any hardware.
Is dry-run protection bad for the pump?
No, it is the opposite: dry running is what destroys submersible pumps, through overheating and wear with no water to cool or lubricate. A protection trip is the system saving the pump. Treat repeated trips as information about the well, not as a nuisance to be overridden.
How do I know if the problem is the pump or the well?
Timing tells you. Problems that follow runtime (fading flow, trips after a consistent interval) point at the well and its recovery. Problems that are identical from the first second of the day, in full sun, point at the pump, the array or the pipework. Note the pattern for a day before pulling anything out of the ground.
Still stuck after the checks above? Send us the symptom pattern, well depth, and your inverter model, and we will help you narrow it down: contact the IDEEI team.