A pump that runs but will not drain is frustrating.
It can also be a messy plumbing problem.
This is common with sealed pump basins.
It can happen with sump pumps.
It can also happen with sewage ejector pumps.
In this case, the pump sits inside a sump casing.
The discharge line connects to a septic line.
The pump worked fine before.
Then the housing needed some jiggling.
The pump would turn on and off.
That made the switch seem like the problem.
So the switch assembly was replaced.
With the housing open, the pump moved water well.
But when the cover was closed, the pump kept running.
Even worse, water came from the vent pipe.
That is an important clue.
What This Problem Usually Means
If water comes from the vent, something is wrong.
The pump may be pushing water into the wrong path.
The discharge pipe may not be connected correctly.
The check valve may be stuck shut.
The check valve may also be installed backward.
A blocked discharge line can cause the same problem.
The pump runs because the basin stays full.
It does not shut off because water cannot leave.
That can overheat the pump.
It can also flood the basin area.
For general pump help, see this sump pump troubleshooting guide from Pentair.
Question And Answer
Question: Why does my pump run but not eject water into the exit pipe?
Answer: The most likely cause is a blocked or disconnected discharge path. Check the discharge pipe, check valve direction, and lid connection first. If water comes from the vent, stop running the pump until the discharge problem is found.
Start With The Discharge Pipe
The first check is the pipe inside the basin.
Make sure it lines up with the lid fitting.
A small shift can break the seal.
This can happen after switching work.
The pump may spray inside the basin.
It may also push water toward the vent.
Look for a loose union or a bad gasket.
Also, check the pipe height.
The cover should not push the pump sideways.
If the cover changes the pump position, fix that first.
Check The Check Valve
A check valve can fail without warning.
It can also get debris inside it.
That debris can hold the flapper closed.
It may have worked before the repair.
But moving pipes can loosen buildup.
That buildup can jam the valve.
Look for an arrow on the valve body.
The arrow must point away from the pump.
It should point toward the septic line.
If the valve is backward, water cannot leave.
Do Not Ignore The Vent Pipe
The vent pipe should carry air.
It should not carry pumped water.
Water at the vent means trouble.
Stop and inspect the basin connections.
If this is a sewage ejector basin, use care.
Wear gloves and eye protection.
Keep the power off while working inside.
For septic safety basics, visit the EPA septic systems page.
Simple Troubleshooting Order
First, unplug or shut off the pump power.
Second, open the basin safely.
Third, check the float switch movement.
Fourth, inspect the discharge pipe connection.
Fifth, confirm the check valve direction.
Sixth, look for a clogged discharge line.
Seventh, test the pump with the lid aligned.
Do not let the pump run dry.
Do not let it run against a closed line.
That can damage the motor.
Final Thought
The new switch may be working fine.
The pump may also be working fine.
The issue sounds like a discharge problem.
Focus on what changed during the repair.
A loose pipe, a shifted lid, or a stuck valve is likely.
If sewage is involved, call a plumber soon.
This is not a leak to leave alone.
I’m Chris Mayer, writing for Plumbing 101.
