I am "attempting" to fix our shower faucet and in feeling ambitious, I decided to take a wrench to the broken knob. To my pleasant surprise, the "cartridge" just popped out and I thought to myself "ok cool, just pop another one in and I'll be good". Unfortunately, there are no identifying marks on the cartridge or any of the hardware associated with the shower. I have spent hours looking online and I still have no idea what brand, let alone model it is. Any ideas would be greatly appreciated. I am looking for the blue/white cartridge in the attached photo.
I'm confused, you have two cartridges in your hand and all the cartridges are in place in the shower valve. Is it a different shower?
If there are no markings anywhere on the valves or handles, You've got two choices: go to your home store and look on the plumbing racks for an identical cartridge (bring the old one with) or go to a plumbing supply store and they should be able to match it. Those guys usually know their stuff. It will be hard to find one online without actually being able to line it up with the old one. Good luck and stay safe out there.