We recently replaced our water heater. We get great hot water flow to our sinks and even to our tub faucet, but when we pull the diverter lever the shower is luke warm even with the faucet handle turned all the way to hot. This was not a problem before the water heater replacement. My first suspicion was the cartridge but it seems that if it is letting hot water through the faucet it should be letting it through to the shower as well.