A water pump that cycles on and off in short bursts (every few seconds to every minute) with no fixtures open indicates either a small slow leak in the system, a faulty pressure switch on the pump, or pressure pulses from a system without an accumulator tank. The most common cause is a slow drip — typically at the toilet or an outside shower fitting.
Most likely causes (in order of likelihood)
- Slow drip leak — toilet flush seal, faucet aerator, or outside shower. Most common cause.
- Failing pressure switch on the pump — switching at wrong PSI, causing rapid on/off cycling.
- No accumulator tank installed — pump cycles every time pressure pulses (normal for low-end systems but can be fixed).
- Air in the system — usually after dewinterizing or refilling fresh tank.
- Worn pump diaphragm — pump can't hold pressure even briefly.
- Loose fittings on the pressure side allowing micro-leaks.
Diagnostic steps (in order, free/cheap before expensive)
- First, confirm cycling pattern: rapid cycling every few seconds usually means missing/failed accumulator or bad pressure switch. Slow cycling every 1-5 minutes usually means a leak.
- Run the dye-in-toilet-tank test (food coloring in the tank, watch for color in the bowl). Most common single fix.
- Inspect every fitting accessible from below sinks and behind the pump for moisture.
- Check outside shower and any low-point drains for slight drip.
- If no leak is found and cycling is rapid, install an accumulator tank inline after the pump ($30-$60 part, fixes cycling instantly).
- If you have an accumulator and the pump still cycles rapidly, the pressure switch on the pump needs adjustment or replacement. Most Shurflo and Flojet pumps have an adjustable screw on the switch — turn 1/4 turn clockwise to increase cut-off pressure.
- If symptoms persist with no leak, no fittings, and a working accumulator, replace the pump.
DIY vs. call a tech
All steps DIY. Accumulator tank install is a 30-minute job. Pump replacement is a 1-hour job.