Pump won't turn on / no pressure buildup
Start with power: confirm the breaker hasn't tripped. If the breaker is fine, a licensed electrician can confirm whether voltage is actually reaching the switch — that check means opening the cover with the circuit live, which is their call, not a DIY one. Assuming power is present, the switch's contacts may be corroded or failed open, or the cut-in point has drifted so low the switch never calls for the pump. On switches with a low-pressure cutoff feature, a tripped cutoff will also look like "won't turn on" — check whether it needs to be manually reset. On Square D switches this is option M4 (M4 among the option letters after the pressure code, with a lever marked AUTO, START and OFF); Square D says it opens the contacts at about 10 psi below cut-in and turns the pump off. See the part number guide. Mineral or sediment buildup under the diaphragm can also mechanically jam the switch in the off position, a failure mode documented in a real terrylove.com case where a stuck diaphragm held cut-in at the wrong pressure no matter how the switch was adjusted (see Sources).
Pump won't shut off / runs continuously
This is the more urgent symptom — a pump that won't stop can overheat and burn out. Likely causes: contacts welded or stuck closed, the cut-out point drifted too high for the pump/tank to reach, or mechanical binding in the switch body. Shut off power immediately if you suspect this rather than let the pump keep running while you diagnose.
The switch is only one of the causes on Franklin Electric's list for a motor that "runs continuously". Its system troubleshooting table names these, with the checks a well professional makes:
| Possible cause | Franklin's check |
|---|---|
| Pressure switch | Check the switch for welded contacts; check switch adjustments |
| Low water level in well | The pump may exceed well capacity: shut off the pump, wait for the well to recover, check static and drawdown level from the well head |
| Leak in system | Check the system for leaks |
| Worn pump | Symptoms are similar to a drop pipe leak or low water level; if the pump shuts off when the switch setting is reduced, worn parts may be the fault |
| Loose coupling or broken motor shaft | Check for a loose coupling or damaged shaft |
| Pump screen blocked | Check for a clogged intake screen |
| Check valve stuck closed | Check operation of the check valve |
| Control box malfunction | Single-phase control box procedure in the manual |
Some of these checks can involve pulling the pump or working inside the control box or switch, which is work for a licensed well professional. Shut the pump off at the breaker, as above, and have one diagnose it.
Pump cycles on and off rapidly (short cycling)
This is usually a tank problem more than a switch problem. A waterlogged pressure tank — the internal bladder has failed and the tank can no longer hold an air cushion — causes the large majority of short-cycling cases. A failing switch, a leak somewhere in the house, a bad check valve, or an undersized tank make up most of the rest. See our dedicated short-cycling guide for the full breakdown and diagnostic steps (tap test, Schrader valve check) before assuming the switch is at fault.
Pressure feels inconsistent or fluctuates
Sediment or mineral buildup under the switch diaphragm — the same failure documented in the terrylove.com case above — can cause erratic readings even when the switch nominally cycles at the right points. A worn diaphragm or a loose electrical connection at the switch terminals are the other common culprits. Cycle the pump a few times while watching a gauge; if cut-in or cut-out shifts noticeably between cycles, the switch itself is the likely source, not your plumbing.
Quick diagnostic checklist
- Confirm the breaker hasn't tripped. Whether voltage is actually reaching the switch is something a licensed electrician can confirm safely — checking it means opening the cover with the circuit live, which isn't a DIY step.
- Watch a pressure gauge through two or three full pump cycles; note cut-in and cut-out each time.
- With power off at the breaker, open the cover and look for corrosion, pitting, or scale on the contacts and diaphragm, then close it back up.
- Tap the pressure tank top to bottom — hollow at top, solid at bottom is healthy; solid throughout suggests a waterlogged tank, not a switch fault.
If the switch adjusts cleanly and the symptom clears, see the adjustment guide. If it's stuck or won't hold a setting, see when to replace instead of adjust.