Diagnose and replace a bad ejection pump switch
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Photo 1: Test the switch
Test the switch by bypassing the piggyback plug and plugging
the pump in directly to see if it works.
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Photo 2: Replace the switch
Use a plastic zip tie to attach the new switch cord to the
pump at the same point the old cord was attached.
When sewage ejection pumps fail, you can quickly have
an ugly mess on the basement floor. Before you panic
and call the plumber (minimum charge $250), make
sure the “float” switch works. Most sewage ejector pumps and
some sump pumps have a floating ball attached to the pump by
a separate electrical cord—if you see two cords coming out of
the basin, you have a float switch. This switch activates the
pump when the water reaches a certain height. The switch is
plugged in with a “piggyback” plug, and the pump is plugged
into the back of it so it doesn't turn on until the switch does
(Photo 1). Unfortunately, these switches may only last half as
long as the pump, according to manufacturers. However, universal
replacement switches are available at home centers and
plumbing suppliers for $20, and replacing the switch is simple.
First check the circuit breaker and GFCI outlet. If they're OK,
unplug the pump from the back of the piggyback plug and plug
it in directly. If the pump kicks on, the switch is bad. If it
doesn't turn on, the pump is bad, but replacing it ($300, including
switch) is just as easy as replacing the switch—simply lift
out the old pump and put a new one in.
If the pump works, run water for a minute to flush out the
dirty water—but don't let the water level go below the pump or
you'll burn out the pump. Then remove the basin top. Pull the
vent pipe from the top and loosen the coupling or union that
joins the waste line together (wrap a towel around the pipe to
catch any water).
Lift out the pump and mark the point where the cord that
holds the switch is attached to the pump. Attach the new switch
at the same point so it will turn on and off at the same water
level (Photo 2). Also check to be sure there's an air bleed hole
near the bottom of the waste pipe (another potential cause of
pump failure). If you don't see one, drill a 1/16-in.-diameter
hole into the waste pipe about 2 in. from where it enters the
Put the pump back in the basin and reassemble the plumbing.
Make sure the float switch moves freely and doesn't get
wedged against the sides. Seal around the edge of the basin with
silicone caulk if the original gasket or seal is deteriorated.
Figure A: Sewage Pump System
When the water
level rises, the
turns on the
grinds waste and
ejects it up the
waste line. The
check valve stops
flowing back into
the basin. The
the pump is