Put a new mixer tap in bathroom bath now no hot water running only cold water
Can anyone help me please

Hi SW

Either someone forgot to turn the hot water supply back on to the valve, OR the hot inlet to the valve (or cartridge) is plugged with sediment/debris. If the water is back on, for sure, then shut the water off, diassemble the valve, pulse the water supply on for a few seconds, inspect the cartridge and see what happens. Something should reveal itself pretty quick!

Mark

I agree with Mark. Start by reinacting how you shut down your water supply to do the replacement. Check that every valve is no open.