Laundry tub w/ejector pump not emptying

I have a basement laundry tub that empties into a sewage ejector pump. The pump is vented and the pump outlet has a check valve and gate valve.

The sink receives the condensate drains from my central air, drain from a dehumidifier, and the washing machine drain.

The whole thing has been in place and working fine for about a year. All of a sudden it has started to act up. At times (not all the time) the sink will stop draining and begin to back up. This can happen with or without the washing machine in use. If we don't catch it it will back up until it overflows.

The fix is simple, just reach under the sink, give the trap a light tap on the bottom and the pump kicks on and drains the sink. Probably have to do this about every other day or so.

I took the trap all apart and it is fine. I have not poked around at the pump yet because I'm not sure what to look for.

Anyone ever see this kind of problem? I'm baffled!!

Thanks for any help you can offer.

Joel

Level switch in the sump? NOt sensing the level, and when you knock things, the switch operates to pump it out?

No level switch, float

This pump doesn't have a fixed level switch, but a float instead. The switch is encased in a plastic float attached to a cord and it just kind of flops around in there.

I did have a problem with the pump being constantly on when I initially installed it and discovered by looking through the inlet hole that the float switch had lodged in the on position during shipping. Once I dislodged it everything worked fine until now.

I guess the float could be stuck in the off positon now, but the tap on the trap that makes it work now is so small and the response so instant that I don't think the float is physically stuck.

Do you think the switch mechanism inside the float could be bad?

Any other ideas?

Thanks for your help.

Joel

pump

The float is not attached to the pipe, so tapping the pipe would not affect a stuck internal switch. The float is getting stuck, possibly by accumlated lint, and tapping the pipe ever so gently dislodges it and lets it turn the pump on.