Hansgrohe PB shower cartridge (brand new) passing water thru cold side with the shower handle turned to off. Six-year old cartridge replaced the other day. Removed side filters and cleaned. O-rings ok. Applied silicon grease and reinstalled. Installed BRAND NEW cartridge, put on valve plate (four screws) and turned cold water back on at valve stops. After about 10 seconds water started coming out shower head. Turned off stop, removed cartridge assy and checked o-rings. Were in place, grease was smeared on filter plate (hot/cold inlets) surfaces. Re-installed again, turned on valve stop and water came out of the shower head at about a pint a minute. Continued to leak until I turned off cold stop. Hot side is from an instant hot-water heater so I can't tell if the hot side is leaking also. You can hear the water flowing through the valve when the valve stop is turned on. Could there be a slight mis-alignment in the valve assy/filter plate inlets and the new cartridge? How would I ever know? Should I have also replaced the plastic filter holders?