Above-Ground Diagnostics
How to tell if a water pump is bad without removing it?
Pulling a submersible pump out of a 300-foot well is the single most expensive hour in well service. It is also entirely avoidable when the fault turns out to be a switch, a tank or a wire. Nearly every question worth asking can be answered with a meter, a gauge and twenty minutes at the pressure tank.
Short answer
You can learn most of what you need from above ground. Start at the pressure switch. If the contacts click but the pump makes no sound, the fault is downhole or in the wiring. If there is no click at all, check the breaker and the switch itself. A clamp meter on the pump leads tells you a lot: zero amps means no power or an open motor, while amps well above the nameplate rating usually means a locked or dragging motor. An insulation resistance test on the motor leads catches a failed winding or a nicked drop cable. A waterlogged pressure tank and a stuck check valve mimic a bad pump, so rule those out first.
The Diagnostic Sequence, In Order
- Breaker and disconnect. Confirm voltage at the pressure switch terminals. No voltage means the problem is upstream of the pump entirely.
- Pressure gauge reading. Zero with the pump idle points at the switch or the pump. Full cut-out pressure with no water at the tap points downstream.
- Pressure switch contacts. Watch them close. If they click and the pump stays silent, power is reaching the switch but not the motor.
- Amp draw with a clamp meter. Compare against the motor nameplate. Zero amps means an open circuit. Amps well over rating means a locked or dragging rotor.
- Insulation resistance to ground. A megohmmeter across the motor leads and the casing finds shorted windings and nicked drop cable.
- Tank air charge. With the system drained, the tank's pre-charge should sit about 2 psi below the switch cut-in. Water out of the Schrader valve means a ruptured bladder.
Those six steps settle the question in the large majority of residential systems without anyone touching the well cap.
Reading What the Tests Tell You
No amps, voltage present at the motor leads: the winding is open or the drop cable has broken. The pump is coming out either way.
High amps, breaker tripping: a locked rotor, a motor full of sand, or a failing start capacitor in a three-wire control box. Test the control box first, because it is the cheap half of that diagnosis.
Normal amps, no pressure built: worn impellers, a hole in the drop pipe, or a well that has drawn down below the pump intake. A water level sounder settles it.
Low insulation resistance: moisture has reached the windings or the splice. Replacement.
If the readings point at the pump, our well pump repair and replacement service covers the pull, the new pump and the post-startup testing.
What Not to Try Yourself
Well circuits are typically 240 volts, and the pressure switch terminals are live whenever the breaker is on. Amp and insulation testing on a live well circuit is licensed work for good reason.
Beyond the electrical risk, Colorado Revised Statutes Title 37 requires that pump installation and repair be performed by a state-licensed pump installation contractor or licensed master plumber. The practical reason is just as persuasive as the legal one: a drop-pipe string released into the casing can destroy a well that cost tens of thousands of dollars to drill. If the house has been without water for more than a few hours, treat it as urgent and call our 24/7 emergency plumbing line.
Talk to a Licensed Pump Technician
Get a Straight Answer About Your Well Pump
Our licensed pump technicians test before they quote: amp draw, insulation resistance, tank pre-charge and water level, with the readings written down.
We serve private wells across Fort Collins, Loveland, Wellington, Laporte, Berthoud, Windsor, Greeley, Estes Park and Red Feather Lakes.
Visit our Well Pump Services page to review the full scope of work and request service.