I recently purchased a rental house. I replaced the hot water heater and shut off valves. With the shutt-off in and out of the tack are closed, I still get cold water from the hot side of all faucets in the house. When valves are open, and temp. Set at very hot, I get semi-hot water.

Hi Jcohlmias...

Sounds like a mixing valve cartridge has gone bad here...

Start by shutting all the hot water shutoffs under all the sinks with single handle faucets... then shut the cold water feed into the water heater. Now, run the water... still have the problem? If so, the issue is probably a cartridge at a shower valve which can't be isolated, but for now, let's assume that issue isn't at the shower valve and is at a faucet.

Start by opening one shutoff at a time... check the hot water each time. When you get cold water out the hot then you have found the valve with the issue. Hope that makes sense. The mixing cartridge would need to be replaced.

Try this.. let us know what you find...

Mark