I installed a hot water heater everything works fine but the shower it has no hot water or preasure can you help me?

Do you have cold water in that shower ? What kind/brand/type of faucet is it ?

I installed a hot water heater everything works fine but the shower it has no hot water or preasure can you help me?
When you installed the new water heater you dislodged some minerals built up in the pipe walls and it got sucked up into your shower valve where it's now blocking the hot water inlet ports of the cartridge. Shut the water off to the shower valve and open it up. Pull the cartridge out and check and clean out the inlet ports on the cartridge. Now turn the hot water back on to flush out the supply and the valve body. Reassemble and test. Good luck, Tom