Originally Posted by Dr_Bean
IF the optical detection fails completely (e.g. because the optics are to dirty)...
I believe the "optical" sensor is using infrared signal and so is not blocked from dust (mud). I think the normal death of these pumps (excluding flooding with salt water or mud) would come either from rupture of the membrane or from Mosfet death that is probably operating the switching. I wonder how long is the life of these two components.