What the pump is doing tells you what is wrong with it. A pump that is silent has a supply problem, a pump that hums without turning has almost certainly lost its start capacitor, and a pump that runs happily while moving no water has lost its prime or is pulling air.
Before you open anything
Turn the breaker off, not just the timer. A pool pump capacitor stores a charge after the power is cut and can still give you a serious shock through a screwdriver. Stop and call an electrician rather than continuing if you find any of these:
- A burning smell, scorch marks, or melted insulation.
- Exposed or damaged wiring, or a conduit that has come away.
- Standing water around the pad or the electrical box.
- A breaker that trips again immediately after you reset it. That is the breaker doing its job. Resetting it repeatedly is not troubleshooting.
Check these first
- The breaker, and the GFCI outlet if there is one. Both can trip without looking tripped.
- The timer or the schedule on a variable-speed pump. A pump obeying a schedule you forgot about is not a broken pump.
- The water level. Below the skimmer mouth and the pump is drawing air rather than water.
- The pump and skimmer baskets, and the lid o-ring. A dry, cracked o-ring is the most common air leak there is.
What it means
Nothing at all: it is not getting power
A silent pump is almost never a dead motor. It is a tripped breaker, a tripped GFCI, a timer that is doing exactly what it was set to do, or a failed contactor or relay. Motors rarely die in complete silence.
What to do Work from the breaker outwards. Breaker, then GFCI, then timer or schedule, then the wiring at the pump. If the breaker trips the moment you reset it, stop there and get an electrician.
Hums but will not turn: start capacitor, or a seized shaft
That hum is the motor energised and unable to start rotating. In most cases the start capacitor has failed, which is a common and inexpensive part. The other possibility is a seized shaft, usually from a motor that has sat unused through a winter or run dry.
What to do With the breaker off, see whether the motor shaft turns by hand. If it turns freely the capacitor is the likely culprit. If it will not budge, the motor has seized and the repair is a different conversation. Capacitors hold a charge, so this is a reasonable place to stop and call somebody.
Runs but no water moves: it has lost prime or is pulling air
The motor is fine. Something on the suction side is letting air in or stopping water getting through: a low water level, a blocked skimmer or pump basket, a dried-out lid o-ring, or a clogged impeller. Air in the pump housing means it has nothing to push.
What to do Fill the pump housing with water and restart it to re-prime. If it loses prime again, look for the air leak rather than repeating the fill: bubbles returning to the pool and a pump basket that will not stay full both point at the suction side.
Loud or grinding: bearings, or cavitation
The sound tells you which. A continuous screech or rumble that gets worse over weeks is bearings wearing out. A rattling sound like gravel going through the pump is cavitation, which means the pump is being starved of water and is a plumbing or water level problem rather than a motor fault.
What to do Cavitation first, because it is cheap to fix and it destroys the pump if left: check the water level, the baskets and the suction valves. Bearing noise is a motor replacement or rebuild, and running it until it seizes does not improve the outcome.
Leaking water: usually the shaft seal
Water dripping from between the motor and the wet end is the mechanical shaft seal, which is a wear part. It matters more than it looks: water tracking into the motor bearings is what turns a cheap seal replacement into a motor replacement.
What to do Deal with it rather than putting a bucket under it. A drip from the lid or a union is a different and easier problem, usually an o-ring, so work out which end it is coming from first.
Stops on its own: thermal overload
The motor has a thermal cutout that shuts it down before it cooks itself, and it restarts once it cools. Something is making it run hot: blocked ventilation, direct sun with no airflow, low voltage, or a pump working harder than it should against a dirty filter.
What to do Clear the vents and anything stacked around the motor, clean the filter, and see whether it still cuts out. A pump that overheats on a clean filter in open air has a supply or motor problem worth getting looked at.
While it is off
Water that is not circulating is not being sanitised, and in warm weather a pool can turn in a couple of days. Test your chlorine before you are dealing with two problems instead of one.
If the pump is being replaced rather than repaired, one thing worth knowing before you shop: horsepower tells you almost nothing about what a pump costs to run. It is a capacity rating, not a measure of demand, and 10 CFR 431.462 calls it motor capacity for that reason. The number that decides your bill is watts at the speed you actually run, which is why our pump energy calculator asks for watts off the display and refuses to derive them from horsepower.