Pump Loses Prime Repeatedly During Cycle: Check Valve & Foot Valve Troubleshooting

A 1.5 HP well pump with a check valve on the inlet and a 6-zone FIMCO hydro-indexing valve loses prime, regains it, then loses it again—cycling throughout the run. The expert suspects a faulty check valve or a suction-side leak.

Diagnostic Steps

1. Inspect the check valve near the pump inlet. If it’s a swing check, the flapper may be stuck or the seat corroded. Replace with a new spring-loaded check valve (same size).
2. Check the foot valve at the bottom of the suction line in the well. Pull the pipe (if feasible) and verify the foot valve opens freely and seals tight. A leaking foot valve lets water drain back, breaking prime.
3. Pressurize the suction line from a garden hose (with the pump off) to find air leaks. Bubbles at joints indicate a leak.
4. Verify the pump’s mechanical seal isn’t drawing air. If the seal is worn, air enters the volute.

Repair Approach

Start with the check valve—it’s the easiest to replace. Cut the PVC, install a new check valve with unions for future service. If the problem persists, pull the suction line to inspect the foot valve. In many cases, a new foot valve (stainless screen, weighted flapper) solves the cycling.

Priming After Repair

After any suction-line work, re-prime the pump fully (fill casing, vent air). The system should then hold prime through all zones.