Pump Runs On Manual But Not On Float Bypass Vs Normal Decision Tree
Why this matters
A pump that runs from the manual override and refuses to run from the float circuit is one of the most useful diagnostic states a septic technician encounters. It rules out the pump itself, rules out the power feed, rules out the breaker, and narrows the fault to the control circuit between the float and the contactor. The decision tree below isolates the broken link in that chain in a defined order so the right part comes off the truck and the panel cover only opens once.
Step 1: Verify what "manual" actually does
Read the panel label and the install drawings. Not all "manual" switches are wired the same way.
- A true HOA (Hand-Off-Auto) selector in Hand position bypasses the float circuit entirely and energizes the pump directly through the contactor.
- A "test" or "momentary run" pushbutton typically energizes the contactor only while held.
- Some panels have a separate test point that bypasses the contactor and runs the pump straight from line.
Confirm which is which. If "manual" bypasses the contactor entirely, you have not proven the contactor is good; you have only proven the pump and the line side of the contactor work. The next test needs to engage the contactor.
Step 2: Re-run "manual" through the normal contactor path
If the panel has a true HOA, leave the selector in Hand and verify the contactor coil pulls in. Listen for the click; watch the contacts. The contactor energized in Hand with the pump running confirms:
- Line power to the contactor.
- Contactor coil good.
- Contactor contacts good.
- Pump and pump cable good.
What remains: the float circuit and anything between the float and the contactor coil.
Step 3: Lift each float and watch the relay
With the selector in Auto, manually lift each float to its actuation position.
- Lift the pump-up float. Listen for the relay or the contactor to pull in.
- Lift the pump-down float to its de-energize position. Listen for the relay to drop out.
- Lift the high-water float. Confirm the alarm relay energizes.
Three possible outcomes:
- All floats actuate their relays. The float circuit is good. The fault is the control logic between the float relay and the contactor coil (a wire, a fuse, an interlock, a timer in a dosed system).
- The high-water float actuates but the pump-up float does not. The pump-up float is failed or the wire to it is open.
- No floats actuate any relay. The float power supply, a control fuse, or the float common is open.
Step 4: Meter the float at its conductor
If a float does not actuate, lift it to position and meter at its terminal on the float strip in the panel.
- A normally open float should read closed (continuity) when lifted.
- A normally closed float should read open when lifted.
- A float showing no continuity change at any position is mechanically failed or has a broken cord.
Confirm the float wiring matches the panel schematic. A float landed on the wrong terminal pair reads as a failed float and is a common installation error that goes unnoticed for years until the panel is replaced.
Step 5: Check the float power supply and control fuse
Many panels run the float circuit at low voltage from a step-down transformer. A failed transformer drops float voltage to zero and no float can actuate the relay regardless of its physical state. Meter at the float common.
- Expected float-circuit voltage per the panel schematic.
- Zero volts at the float common with line voltage on the transformer primary means the transformer is open.
- A control fuse on the secondary side blown reads identically and is the cheap-and-fast first check.
Step 6: Check the timer or dose logic on dosed systems
On a time-dosed system, the float calls for a dose, but the timer's on-cycle determines whether the contactor actually pulls in at that moment. A timer with the on-cycle stuck at zero, a timer with a failed output relay, or a timer in an off-mode setting will leave the pump silent when the float calls.
- Read the timer's on-time and off-time settings against the design.
- Force a manual dose at the timer if the panel supports it.
- Swap to a known-good timer if available.
The timer is a frequently overlooked link in the chain because it is invisible in conventional demand-dose systems.
Step 7: Check the interlocks
Some panels include interlocks that block pump operation under fault conditions.
- A high-water lockout that has latched and not been reset.
- A pump-protection thermal that latched and requires a manual reset.
- A door-position interlock on a wall-mounted panel that has stuck open.
- A remote enable (alarm dialer or BMS) that has dropped the run-enable signal.
A latched interlock satisfies "pump runs in manual but not in auto" perfectly because manual bypasses the interlock chain. Read the panel manual.
Step 8: The wire between the panel and the pump chamber
A panel-to-chamber control cable that has been damaged by a mower, by ground settling, or by rodent gnawing in a wet pit can break a float conductor while leaving the pump-power conductors intact.
- Inspect the cable run from the panel exit to the chamber.
- Look for visible damage at any pull-box or grommet.
- Continuity-test each float conductor at the panel against the float terminal in the chamber.
A broken float conductor is a more common cause than a failed float on systems older than a decade.
Decision tree summary
- Define what manual actually bypasses.
- Re-run manual through the contactor to clear the pump and contactor.
- Lift each float and observe its relay.
- Meter the failing float at the panel terminal.
- Check float power supply and control fuse.
- On dosed systems, audit the timer.
- Read the interlocks for latched faults.
- Inspect the panel-to-chamber control cable.
A pump that runs in manual but not on float is a tractable problem. Eight gates in order get you to the broken link without parts-cannon guessing.
A pump chamber riser is wet, often above an energized cable, and is a confined space. Lock out the breaker at the panel before reaching in. Test for H2S before opening; ventilate the chamber and work from the rim.
References
- US EPA, SepticSmart resources, https://www.epa.gov/septic
- US EPA, Decentralized Wastewater Treatment Systems Manual, pumping and control chapters
- NSF/ANSI 40 and NSF/ANSI 245 onsite residential wastewater treatment standards