PLEASE HELP!!! My plumber replaced both GP77759 and GP500520 Kohler shower cartridges and now the water flow rate in the showers is very low. The flow rate was excellent prior to him simply replacing the cartridges with brand new ones. Plumber has no clue how to fix it. Flow is completely fine in the rest of the house and remains unchanged. ONLY in the two valves where he replaced the cartridges is the flow reduced from previously. I desperately need this fixed!! No one at the company has a clue either. Please help!
Remove the shower head and see if you get good flow.
Sometimes the work on the pipes dislodges crud and it clogs filters and outlet valves.
If the flow without the shower head is good, clean the screens and the holes in the head. If the flow without the shower head is still poor, have the plumber check for clogging in the cartridges and replace them if needed.