Replacing Kohler K-78913 cartridge in K-400 thermostatic mixing valve

[jspitt]

The Kohler K-400 mixing valve in one of our showers stopped working (hot only a trickle, cold with regular pressure) so I thought I'd try to replace the mixing valve cartridge, thinking it must be fouled. A replacement cartridge is on the way from Kohler, and in the meantime I thought I'd get ready by removing the existing cartridge. I've shut off the hot and cold stop valves a nd then tried to remove the cartridge using a deep 11/16" socket, then a pipe wrench (see photo 1). The cartridge didn't give at all under strong torque. I managed to chew up the brass a little using the pipe wrench. To complicate things, it appears the plumbers who installed the mixing valve did not fasten the valve to any blocking (see photo 2). So I am concerned about breaking something by applying too much pressure. Does anyone have any advice on removing the cartridge? Thanks in advance for any suggestions.

P.S. There is some blocking behind the valve, and I think I can drive a couple of screws in the hold the valve, so that may not be as much of an issue as I previously thought.

 

[Smooky]

If you can secure the valve that would be good. I would put a section of pipe over the wrench handle so you can get more leverage.

 

[Sponsor]

 

[jspitt]

Thank you, Smooky. Success. I was able to drive in four screws to fix the valve body to blocking behind the valve. I then used a piece of 3/4" galvanized pipe to increase leverage as you suggested (see photo 3) and was able to remove the cartridge with no problem (and without breaking anything!).

 

[Smooky]

Great! I’m glad it worked out for you. Thanks for the follow up!

 

[Prometheis]

The Kohler K-400 mixing valve in one of our showers stopped working (hot only a trickle, cold with regular pressure) so I thought I'd try to replace the mixing valve cartridge, thinking it must be fouled. A replacement cartridge is on the way from Kohler, and in the meantime I thought I'd get ready by removing the existing cartridge. I've shut off the hot and cold stop valves a nd then tried to remove the cartridge using a deep 11/16" socket, then a pipe wrench (see photo 1). The cartridge didn't give at all under strong torque. I managed to chew up the brass a little using the pipe wrench. To complicate things, it appears the plumbers who installed the mixing valve did not fasten the valve to any blocking (see photo 2). So I am concerned about breaking something by applying too much pressure. Does anyone have any advice on removing the cartridge? Thanks in advance for any suggestions.

View attachment 39975 View attachment 39976

P.S. There is some blocking behind the valve, and I think I can drive a couple of screws in the hold the valve, so that may not be as much of an issue as I previously thought.

Where are these odd sized cartridges coming from ? The one I just measured was an 18 mm hex, NOT 11/16ths ....

 

[Reach4]

11/16 is 17.46 mm. So an 18 mm hex socket would probably work on 11/16.