Should a check valve stop all backflow?

[dbb1]

I've noticed some behavior from my new system that surprises me. On the ground next to my new furnace is a condensate pump that receives water from coil, furnace, and humidifier. Right now the humidifier runs a lot so I can really observe how the pump behaves.

The clear outlet tube from the pump goes up to roughly ceiling height, then over a bit, then straight down to where it drains into some vertical PVC pipe.

Because the end point of the clear outlet tubing is way above the pump itself, I wouldn't expect significant siphoning of water. The pump manual does, however, claim to have a check valve at the point where that tubing connects. I thought that would prevent backflow into the pump when it is off. What I observe is that over time (maybe 10 minutes total), the vertical column of water slowly sinks back down to the pump, presumably returning the water to the pump's internal tank, since there's no water leak to the floor.

Is this the expected behavior? Should I care?

[t527ed]

sounds like the check valve may have some debris in it, water should not drain back into pump.

[dbb1]

sounds like the check valve may have some debris in it, water should not drain back into pump.

Huh. This is a brand-new pump. I guess I'll call the contractor about it. Thanks!

[firecontrol]

The check valves in these pumps are not precision parts produced to close tolerances. Basically they consist of a plastic ball held to a plastic seat by a light spring. A very slow drain back of water to the pump's tank wouldn't surprise me.

The amount of water held in a 8' column of 3/8" tubing is approximately 5 oz's. This little bit of water seeping back into the pump over minutes is not something to worry about.