Pump Runs on Manual But Not on Float Control: Decision Tree

Why this matters

A sump or sewage ejector pump that runs when manually energized but never starts on its float is the classic split between a healthy pump and a failed control. The manual run proves the motor, the impeller path, the power supply, and the discharge are good. What it does not prove is the float switch, the float's freedom of travel, and the switch wiring that is supposed to start the pump automatically. The common error is condemning the pump (the expensive part) when the cheap control is at fault, or replacing the float without confirming the float is actually the failure and not a wiring or basin-geometry problem. Recognizing that a successful manual run shifts the entire diagnosis to the float-control branch is the whole game.

Symptom presentation

The complaint is a basin that fills and overflows (or a high-water alarm) while the pump sits idle. When the tech lifts the float by hand, plugs the pump straight into power, or uses the piggyback plug's manual position, the pump runs strong and pumps the basin down normally. Returned to automatic/float control, it never starts as the water rises. On a tethered or vertical float, the float may be visibly hung up, waterlogged, or tangled; on a piggyback switch the pump plug may not be seated into the switch piggyback correctly.

Quick checks

• Manually lift the float fully and watch for pump start. If it starts on a manual float lift but not on rising water, the float is obstructed or set wrong. If it does not start even on a full manual lift, the switch or its wiring is dead.
• Inspect float travel: a tethered float tangled on the discharge pipe, cord, or basin wall, or wedged against the wall in a too-narrow basin, never reaches its on-angle. A vertical float rod that binds does the same.
• Check the float for waterlogging (a heavy, water-filled float that no longer rises).
• On a piggyback switch, confirm the pump cord is fully seated into the switch's piggyback receptacle and the switch cord is in the outlet.

Isolation tree

The pump runs on manual, so the fault is in the float-control branch.

• Branch A: Float obstructed / hung up. The float cannot reach its on-position because it is tangled on the discharge pipe, cord, alarm float, or basin wall, or the basin is too small for the tethered float's swing. Free the float, re-route the cord, or convert to a vertical float in a tight basin. Most common cause.
• Branch B: Float waterlogged. The float has taken on water and no longer floats up to trigger. It feels heavy and sits low. Replace the float switch.
• Branch C: Float set at the wrong level. A tethered float with too long a tether, or a vertical float set too high, never reaches its trigger point before the basin overflows. Re-set the tether length / float collar to the correct on/off levels.
• Branch D: Switch contacts failed. Lifting the float fully by hand still does not start the pump, but a direct manual power feed does. The switch's internal contacts are dead or the piggyback receptacle is bad. Replace the switch.
• Branch E: Wiring / piggyback fault. The pump cord is not seated in the piggyback receptacle, or the switch cord/wiring is open. Re-seat and verify continuity through the switch path.
• Branch F: Control panel / relay (on panel-controlled systems). On a duplex or alarm-panel system, a failed control relay or panel float input leaves the pump idle though it runs on hand/manual. Test the panel's float inputs and relay.

Confirming diagnosis

• Obstruction: physically cycle the float through its full arc by hand; if it catches, binds, or fouls before reaching the on-angle, the obstruction/geometry is confirmed.
• Waterlogging: remove and shake the float; sloshing water inside confirms a flooded float.
• Dead switch: lift the float fully and meter continuity across the switch in the on-position. No continuity at full travel confirms a failed switch (the pump already proved good on manual power).
• Level setting: measure the basin on/off levels against the discharge inlet height; a trigger level above the inlet confirms a misset float.
• Panel: simulate the float input at the panel; no pump call confirms a panel/relay fault.

Remediation

Fix the control branch the tree isolates. Free or re-route an obstructed float and secure the float cord and discharge so the float has clear swing room through its full arc; in a basin too narrow for a tethered float to swing, fit a vertical float that travels straight up and down. Replace a waterlogged or contact-failed float switch with the correct type and rating for the pump's amp draw and the basin geometry. A piggyback switch must be rated to carry the pump's running and locked-rotor current, or its contacts burn and fail to start. Re-set tether length or vertical-float collar so the on level is below the inlet invert and the off level keeps the pump body submerged enough to stay primed without dry-running. On panel-controlled systems, replace the failed relay or correct the float input wiring. After repair, fill the basin with water (not by hand-lifting the float alone) and confirm automatic start at the on level and stop at the off level through a full cycle, then verify the high-water alarm trips at its set level if one is fitted.

References

• Uniform Plumbing Code (UPC) / International Plumbing Code (IPC) provisions on sumps, sewage ejectors, and pump basin/venting requirements.
• NFPA 70 National Electrical Code (pump circuit, GFCI/receptacle, and control wiring requirements).
• Pump and float-switch manufacturer service literature (float type selection, basin sizing, on/off level setting, amp ratings).
• Hydraulic Institute / sump-and-sewage pump application guidance for basin geometry and float clearance.