Short answerWork from the panels to the outlet: check voltage at the controller in full sun, then the float switch and any low-water probe, then the intake and the pipe for air or leaks. Most faults are low voltage, no water at the intake, air in the line, a stuck float or wear.
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Key takeaways
- Work from the panels to the outlet: voltage, intake, air, float switch, wear.
- A multimeter and a five-gallon bucket answer most questions in minutes.
- If the water table has dropped, your total dynamic head has risen: recalculate.
Safety. Panels and batteries can deliver dangerous current. Follow NEC Article 690 and local code, and use a licensed electrician or well contractor where your state requires one.
Symptoms and causes
| Symptom | Check first | Then |
|---|---|---|
| Will not start in full sun | Voltage at the pump or controller with a meter; float switch position | Blown fuse, loose connector, controller fault, seized pump |
| Starts late, stops early | Array voltage at low sun vs the pump's start voltage | Add a panel in series, or use a pump controller with MPPT |
| Runs but pumps nothing | Water level vs intake; surface pump prime and foot valve | Air leak on the suction side, worn diaphragm, broken drop pipe |
| Starts and stops repeatedly | Dry-run probe tripping as the well draws down | Lower the pump, reduce flow, or accept cycling on a low-yield well |
| Less water than last year | Shade, dirty panels, clogged intake screen | Worn diaphragm or stator, falling water table, leak in the line |
| Pump runs, tank never fills | Leak or open valve between pump and tank | Head now beyond the pump's curve (water level dropped) |
| Battery system dies overnight | Battery state of charge at dusk; charge controller logs | Array too small for the season; battery too cold to charge |
Measuring is faster than guessing
A cheap multimeter answers most questions in minutes. Measure open-circuit voltage at the array, then voltage at the pump while it runs. A big drop between the two means undersized cable or a bad connection. For flow, time how long the outlet takes to fill a five-gallon bucket at midday: 60 divided by the seconds, times 5, is gallons per minute.
When it is the well
If flow drops and the pump checks out, measure the water level. Water tables move with drought and with neighbouring pumping. If the pumping level has fallen, the total dynamic head has risen, and the pump may now be near the end of its curve. Recalculate with the sizing calculator.
Put your own gallons, lift and pipe in and see every step of the working.