I put in a new cartridge and now my hot water side is luke warm at best. What did I do wrong?

Hello Madman4,

You have to start your own post that it will have more visibility, and please tell us some more about you faucet the Brand and the model number, Thanks.

John

Did you turn the water when you had the valve open to flush out the supplies? No? Then you most likely have some trash clogging the cartridge,
Turn the water off, open the valve and pull the cartridge, Check and clean the inlet ports on the cartridge. Now turn the water back on to flush out any mineral buildup. Reassemble and test, Better now? Good luck, Tom