Pumps very rarely fail without warning. What usually happens is that they warn nobody who is listening. A bearing that will seize in March starts whining in January; a motor that will burn out in summer starts drawing three per cent more current in autumn. This guide is a field checklist for catching those signals while they are still cheap to fix.
Listen: the noises and what they mean
| What you hear | Most likely cause | Urgency |
|---|---|---|
| Gravel or marbles rattling inside the casing | Cavitation – the pump is starved of water on the suction side | Immediate |
| Steady rising whine or growl | Bearing wear | Weeks |
| Rhythmic knocking in time with rotation | Bent shaft, damaged impeller or coupling misalignment | Days |
| Squeal on start-up only | Belt slip or dry mechanical seal | Weeks |
| Loud hum with no rotation | Seized rotor, failed capacitor or single-phasing | Immediate – switch off |
Cavitation deserves special attention
That gravel sound is vapour bubbles forming in the low-pressure zone at the impeller eye and collapsing violently a few millimetres later. Each collapse removes a microscopic piece of metal. Left running, cavitation will pit an impeller into scrap in a matter of months and destroy the bearings through vibration.
Common causes are a blocked suction strainer, a partially closed suction valve, a dropped water level, or a suction lift that was always marginal – particularly at Highveld altitude, where there is less atmospheric pressure available to push water into the pump. If the pump is a surface unit struggling on a falling water source, the real fix is often a different pump type; see surface pump versus submersible pump.
Watch the gauges: pressure and flow
Falling delivery at the same pump speed means one of three things: less water is getting in, less water is getting out, or the pump has lost its ability to generate head. Work through them in that order.
- Suction side. Check strainers, foot valves and suction line joints. On a borehole, check the water level – a seasonal drop is the commonest cause of reduced delivery and is not a pump fault at all.
- Discharge side. Scale, biofilm or a partly closed valve. On irrigation systems, loaded filters are the usual culprit and will show as a rising pressure differential across the filter bank.
- The pump itself. Worn impellers and wear rings let water recirculate inside the pump instead of moving forward. This shows as a permanent loss of head that no amount of valve adjustment recovers.
Keeping a simple monthly log of delivery pressure and flow turns a vague impression that things are weaker into a graph with a slope, which is what lets you schedule a repair rather than react to a failure.
Measure the current: the single best early warning
A clamp meter on one phase, read monthly and written down, will tell you more about pump health than any other single measurement. Motor current tracks the mechanical load, so it moves before anything else does.
| Current trend | Interpretation |
|---|---|
| Slowly rising over months | Bearing drag, impeller rub, or scaling increasing the load |
| Sudden rise | Blockage, debris in the impeller, or mechanical damage |
| Falling with falling flow | Worn wear rings – the pump is recirculating rather than pumping |
| Unbalanced between phases | Supply fault, failing contactor or a winding problem |
| Above nameplate full-load amps | Overload – investigate before the overload relay does it for you |
Look: seals, leaks and vibration
- Drips from the mechanical seal. A few drops per minute on a packed gland is normal and necessary for lubrication. Any visible leak from a mechanical seal is not; it means the faces are damaged and the seal is on borrowed time.
- Rust streaks below the pump. Evidence of a leak that dries between runs. Trace it before it reaches the bearing housing.
- Oil discolouration. Milky oil in a seal chamber or gearbox means water ingress. Change it and find the path in.
- Visible vibration. If you can see the pump moving or a coin will not stand on the casing while it runs, you have imbalance, misalignment or a failing bearing.
- Heat. A motor casing too hot to keep a hand on for five seconds is running above its design temperature. Check ventilation, voltage and load.
Behaviour: cycling, tripping and slow starts
How a pump switches on and off says as much as how it runs.
- Short cycling – starting and stopping every few seconds – usually means a waterlogged pressure tank, a failed bladder, or too narrow a pressure differential. Every start is a thermal shock to the motor, so this is not a cosmetic problem.
- Nuisance tripping of the overload or earth leakage points at insulation breakdown, a damaged submersible cable, or moisture in the motor.
- Slow or laboured starting on a single-phase motor is a failing start capacitor – cheap, and much cheaper than the winding it will take with it.
- Running but not delivering on a surface pump means lost prime: a leaking suction joint or a failed foot valve.
Water quality changes
Sand in the strainer, cloudy water that was clear, or air spitting at the outlet are all pump-relevant. Sand means an abrading borehole or a pump set too close to the hole bottom, and it will wear impellers fast. Air means a leak on the suction side or a water level approaching the pump inlet. Neither is a water problem; both are pump problems in the making.
A simple maintenance schedule
| Interval | Action |
|---|---|
| Monthly | Log running current, delivery pressure and flow. Listen to the pump. Check for leaks. |
| Quarterly | Inspect strainers and filters, test the dry-run cut-out, check contactors and terminal tightness. |
| Six-monthly | Grease bearings where fitted, check alignment and belt tension, sample the water. |
| Annually | Insulation resistance test, full electrical inspection, borehole water level check. |
| Three to five years | Strip and inspect: wear rings, impellers, seals, and on boreholes the rising main and safety rope. |
When a symptom means replace, not repair
Repeated failures of the same component, a pump that has lost more than about 20 per cent of its original head, or a unit whose repair bill approaches half its replacement cost are all signals to stop spending. Our guide to repairing versus replacing a water pump sets out the arithmetic, and if efficiency is the concern, reducing pump energy consumption is worth reading before you buy a like-for-like replacement.
Book a pump inspection. Our field technicians carry out scheduled servicing, condition checks and emergency repairs across Gauteng and beyond – with loan units available so you are never without water. See our service offering, get in touch, or call +27 (15) 516-4991.