We have a grinder pump system for our basement. The pump will come on even when no one is using either the shower or the toilet. Also, I have noticed that it runs when we get a significant rain. I have a conventional sump pump right next to the grinder well. Are there any reasons the grinder well would be affected by rain?

Hi Jim:

Only reason I could think of would be if there is a break in the grinder pump basin underground. Are you sure that there is nothing connected to the pump from the upstairs by chance? I've seen that plenty of times. I'd double check and make sure all the pipes connected are actually from the basement... could be that one of the "VENT" pipes is actually a kitchen sink from above..? Maybe?

Otherwise, I'm thinking the new basin could be compromised and may need to be replaced. Check all piping connections by running all the fixtures upstairs first... see if the pump turns on.

Back to you...

MARK