Quick answer
A pump that will not switch off has lost pressure somewhere on its outlet side. The three usual causes are a hidden leak, a failed non-return valve letting water run back, and a faulty pressure switch that never sees the cut-out point. Whatever the cause, a continuously running pump is destroying itself — the motor and seals are not designed for uninterrupted duty.
Common causes
- Hidden leak on the pressurised side of the system
- Failed non-return valve allowing water to flow back to the tank
- Pressure switch out of calibration or with welded contacts
- Waterlogged bladder tank with no air cushion left
- Tank level low enough that the pump is drawing air
- Toilet inlet valve or outside tap left running, which looks like a fault but is not
What you can do now
- 1Switch the pump off at its isolator for ten minutes and listen for hissing or running water
- 2Close every tap and check the water meter for movement
- 3Check the backup tank level; a pump drawing air behaves exactly like this
- 4Feel the pump body — a pump that has been running continuously will be very hot
- 5Leave it switched off until it is diagnosed rather than letting it run
When to call a professional
Same day. A continuously running pump burns out its motor and seals, and it adds up on the electricity account while it does. Switch it off at the isolator in the meantime. A plumber will pressure-test the outlet side to separate a leak from a valve or switch fault, which is the difference between a small repair and a new pump.
Typical cost in Johannesburg
Pump diagnostic R750 · Pressure switch R650 · NRV R450
Indicative ranges only. We provide written, itemised quotes before any work.
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