A steady sump alarm means water in the pit rose past the alarm float, above where the pump should have started. The pump may have lost power, a float may be stuck, or the discharge may be blocked. A short chirp every so often usually means the alarm's backup battery is low, not high water.
What the sound is telling you
The type of sound tells you which problem you have: high water, a low alarm battery, or a fault on a backup system.
A steady horn with a light. This is the high-water alarm. On Liberty Pumps' ALM-series alarms, the sensor on a sump system is set "such that the activation point (the bump on the right) is slightly higher than the pump activation point." Once it sounds, Liberty says "it will continue to sound until the water level is lowered." The horn is loud on purpose: Liberty rates it at 86 dB at 10 feet.
A short chirp every so often. That's usually the alarm's own backup battery. Liberty says "When the 9V battery is low, the alarm will emit a short chirp about twice per minute." Its alarms carry a 9-volt battery so they keep watching the pit during a power outage. Replace the battery, and the chirp stops. Liberty's schedule is to replace it whenever the low-battery light is on "or every 12 months."
An alarm from a battery backup pump's controller. Backup systems watch themselves and sound off for faults. Zoeller's DC backup manual says "If the DC pump is unplugged or jammed, for example, a fault alarm will result." A missing or unplugged float also sets it off. After the backup pump actually moves water, Zoeller's controller keeps its light and alarm on to show "that the pump ran and pumped water," usually a sign the main pump didn't keep up. Our page on whether you need a battery backup sump pump covers how these systems work.
What to do right now
Start with safety, because a flooded pit and electricity don't mix.
- 1Don't step into standing water near the pit. Liberty warns that "submerged electrical connections can energize the water." If the floor around the pit is wet, shut off the pump's circuit at the breaker before you get close.
- 2Look and listen at the pit. Is the pump running? Humming? Silent? That answer points to the cause below.
- 3Check power. A silent pump often means a tripped breaker or GFCI outlet. Reset it once. If it trips again right away, read why a sump pump keeps tripping the GFCI before you keep resetting.
- 4Silence the horn if you need to, but don't ignore it. On Liberty's alarms, "The alarm will stay silenced for 6 hours after the Silence button is pressed." The water is still there. The silence button just buys you time to fix the cause.
- 5If the pit also takes sewage, meaning it's an ejector basin with a sealed lid, stop running water in the fixtures that drain into it until the pump is working again.
The usual causes of a high-water alarm
Match what you saw at the pit to this list. Liberty's troubleshooting table in its sump pump manual lists most of these.
The pump is silent. Power is the first suspect. Liberty lists "Tripped circuit breaker, tripped GFCI, blown fuse, or other interruption of power." Next is the float. If the float can't move, the pump never gets the signal. Liberty's fix is to position the pump or float switch so it has "adequate clearance for free movement." A float can hang up on the pit wall, a cord or a tipped pump. Wayne notes that vibration can tip a pump over, which "can jam the float so it can't activate the pump." If power is good and the float moves freely, the switch or motor may have failed; see why a sump pump won't turn on.
The pump runs or hums but the water doesn't drop. Water has nowhere to go. Liberty's list for "Pump runs or hums, but does not pump" includes a blocked or restricted discharge line, a "Check valve stuck closed or installed backward," a closed gate or ball valve, a clogged inlet screen and an airlocked pump. For an airlock, Liberty says to turn the pump off and let it sit for several minutes, then restart.
The pump runs constantly and still falls behind. Either water is coming in faster than the pump can move it, or the pump is worn out. It's also possible the check valve leaks and the same water drains back into the pit. Our page on a sump pump that runs constantly walks through that one.
The pump starts and stops on its own. Wayne's manual says its pumps have a thermal protector that "may restart unexpectedly," and that tripping points to "motor overloading as a result of operating the pump at low heads, excessively high or low voltage, inadequate wiring, incorrect motor conditions, or at the end of product life." A pump that keeps overheating needs its cause found.
When the alarm itself is the problem
Sometimes the pump is fine and the alarm is off. Check these:
- Alarm float set too low. If it sits at or below the pump's "on" level, it sounds every cycle. Liberty places the alarm point slightly above the pump's activation point.
- A low 9-volt battery. The chirp, covered above.
- A backup controller reporting on itself. A missing float, an unplugged backup pump or a backup that recently ran all set off Zoeller's controller, even when the pit is dry now.
Test the alarm on a schedule so you trust it when it sounds. Liberty's instruction is to "Test the alarm system every 6 months." Its test is simple: raise the water in the pit above its normal level, or hold a cup of water up to the float, and the alarm should sound. Our page on how to maintain and test a sump pump pairs that with the pump checks.
One more detail from Liberty's pump manual: "If an alarm is used, it must be connected to a separate electrical circuit." That way a tripped pump circuit doesn't also kill the alarm meant to warn you about it.
When to call a plumber
Call if the pit keeps rising and you can't find a power or float problem, if the pump hums without pumping, if the check valve or discharge line needs to come apart, or if the pump is old and overheating. If the GFCI or breaker keeps tripping, an electrician should look at the circuit. And if the alarm has gone off more than once this season, treat that as a pattern: the pump may be too small for the inflow, or it may be near the end of its life. Wondering whether your home needs one at all? Our page on whether an Arizona home needs a sump pump explains where they show up.
HQ Plumbing & Air is available 24/7 for plumbing emergencies, licensed and insured, with free estimates and upfront pricing. If water is already on the floor, shut off power to that area first and call.