I am running a number of Penquin HOBs and the impellers get worn out in 3-4 years. They still pump water but make unbearable noise. The only remedy is to replace them with new impellers but they don't come cheap. Manufacturers typically price replacement impellers at nearly half the price of new filters. Do you know any place that sells cheap replacement impellers. I notice many impellers are interchangeable with different brands, so they don't need to be manufacturer original.
