Your solar pump ran fine for a season — then the controller beeps, display shows “dry run”, and no water flows even though the bore had water last week. Or worse: the pump never stops until the motor smells hot. Both paths lead to the same part of the system: dry run protection, float switch / level sensor, and wiring between them.
This guide covers how dry run works, field fixes farmers can check safely, wiring mistakes, and dealer warranty under PM-KUSUM — without pretending every fault is DIY.
Opening high-voltage DC combiner boxes or mains-linked controllers without training is dangerous. Do low-risk checks (water level, float movement, error codes) yourself; call empanelled electrician / dealer for terminal work.
What the solar pump controller actually does
A solar pump set includes:
- PV array → DC or AC drive (controller/VFD) → submersible motor
- Dry run sensor — float switch, electrode probe, or current-based software in drive
- Optional remote / GSM monitoring on newer PM-KUSUM kits
The controller matches motor frequency to available sun power. When water is absent, motor current pattern changes or the float opens a contact — drive trips to save the motor.
BIS-compliant pumps under PM-KUSUM Component B expect this protection — bypassing it can void subsidy-linked warranty.
Dry run error when water still exists — top causes
| Cause | Field sign | Fix direction |
|---|---|---|
| Float stuck | No movement in tank/well | Clean, reposition, replace float |
| Water table dropped | Sensor above new level | Lower sensor or deepen bore (long-term) |
| Foot valve blocked | Dry run at start every morning | Service valve, de-silt |
| Air lock | Spluttering then trip | Prime line, check leaks |
| Wrong sensitivity | Trip under low sun | Adjust parameter per manual — dealer help |
| Loose wire | Intermittent fault | Tighten in junction box |
| Failed electrode | Corrosion on probe | Replace sensor |
Always confirm actual water at intake with a weighted line or local knowledge — not guesswork.
Float switch vs electrode vs software dry run
Float switch (most common on farm installs)
- Ball float on cable in tank or well chamber
- Mercury or micro switch changes contact when water low
- Pros: Simple, cheap
- Cons: Jammed by mud, rats chew cable, tangled in pipe
Install tips:
- Mount where minimum operating level is clear
- Free cable length — not pinned to pipe
- Drip loop so water does not enter junction box
Electrode sensors
- Probes in well detect conductivity between levels
- Sensitive to mineral buildup — scrape gently in maintenance
Current-based (software) dry run
- Drive reads motor amp curve — no external float
- Must be commissioned by trained installer; wrong pump model setting causes nuisance trips
Wiring — where farmers and local electricians go wrong
- Wrong terminals — dry run input confused with remote start or tank full
- NC vs NO reversed — always trips or never trips
- Shared neutral with pump power causing noise trips
- Long unshielded cable run parallel to motor cable — interference
- Water in junction box — corrosion, random faults
Safe wiring checklist
- Power off at DC isolator / AC breaker before opening controller
- Photo existing wires before disconnecting
- Use manufacturer colour diagram for your drive model
- Crimp or solder + heat shrink — twisted bare wire fails in monsoon
- Label “dry run float” for next season
If your PM-KUSUM dealer installed float in overhead tank but you pump direct to field, dry run may never see bore level — ask to relocate sensor to source, not destination.
Step-by-step troubleshooting (farmer-safe)
- Read fault code on drive display — note letters/numbers for dealer
- Check sun — some drives show dry run when VDC too low; distinguish codes
- Manual float test — lift float gently; does display change?
- Listen at bore — cavitation sound = no water at impeller
- Run at midday once — rule out low-light undercurrent trip
- If still fault → call empanelled dealer with code photo
Do not repeatedly force restart every 5 minutes — heat builds in motor.
Controller failure vs sensor failure
| Symptom | Likely part |
|---|---|
| Float works, still trips | Drive board or parameter |
| Never trips, motor overheats | Sensor bypassed or dead |
| Random trips in rain only | Wet junction / insulation |
| All LEDs dead | DC fuse, lightning surge — warranty claim |
Lightning and poor earthing destroy drives — common in open fields. Surge protection is worth the cost after first failure.
PM-KUSUM dealer warranty — what to expect
Under Component B, your empanelled vendor typically owes:
- Installation workmanship — often 1–2 years
- OEM warranty on motor (multi-year) and controller (check card)
- Response SLA in state tender — varies
Claim pack
- Sanction letter + beneficiary ID
- Serial numbers — motor, drive, modules
- Fault photos / video with date
- Service ticket number
If dealer stalls >15–30 days, escalate to state nodal agency with ticket proof. Subsidy does not replace OEM warranty — but nodal pressure often unlocks spare parts.
See pump cost guide by HP and why savings may disappoint for sizing and expectations.
Prevention calendar
| When | Action |
|---|---|
| Pre-summer | Test float, clean foot valve |
| Monsoon | Seal junction boxes |
| Post-harvest | Check cable for tractor damage |
| Yearly | Dealer inspection if bundled |
Link with PM-KUSUM guide and Component C grid issues if your pump is grid-tied.
Bottom line
Solar pump controller “failure” is often dry run sensor, float switch, or wiring — not a dead motor. Fix water truth first, then float movement, then terminals. Under PM-KUSUM, use empanelled dealer warranty for drive faults — do not bypass protection to “get one more hour of water”.
Protect the motor; it costs more than a float.
Disclaimer: Electrical work carries shock risk. Follow manufacturer manuals and local codes. Warranty terms vary by OEM and state tender. Ask Kisan is not a certified electrician or MNRE agency.
Last verified: June 2026.
Frequently asked questions
What is dry run protection on a solar pump?
Dry run protection stops the pump when water is not available at the intake — preventing motor burn from running without load. Solar pump controllers (VFD/drive units) read dry-run sensors, current draw, or float switches and shut down or restart after a delay. It is essential for borewells with falling water tables.
Why does my solar pump show dry run error even when water exists?
Common causes: faulty float switch or electrode sensor, wrong sensitivity setting, air lock in pipe, silt choking foot valve, loose sensor wiring, or sensor mounted too high after water table dropped. Check physical water level before blaming the controller.
How should a float switch be wired to the controller?
Follow the manufacturer diagram — typically NC/NO contacts go to dedicated dry-run terminals on the drive. Use screened cable if specified, secure connections in a dry junction box, and keep float free to move without hitting bore casing or stones. Wrong terminal wiring triggers false dry run.
Can I bypass dry run to force the pump on?
Bypassing dry-run protection risks burning the submersible motor and voiding warranty. Never bridge the sensor permanently for 'more water'. Fix the sensor, water level, or settings instead. PM-KUSUM empanelled vendors must install protection as per BIS pump standards.
How do I claim warranty on a failed controller under PM-KUSUM?
Keep installation certificate, subsidy sanction letter, serial numbers, and fault code photos. Contact the empanelled dealer first — controller is usually under OEM warranty (often 2–5 years for drive, longer for motor depending on brand). Escalate to state nodal agency if dealer delays beyond documented SLA.