One number of photo copy machine drum cartridge

This code is almost always a false code. I would try clearing it by entering the following key sequence:
Press "Clear" then "Exposure Mode" then "Clear" then "Exposure Mode" (Note that the exposure mode key is the far left key and that these 4 keys must be pressed within 4 seconds)
The display should have gone blank if these 4 keys were pressed properly.
Now enter 14 as if you were making 14 copies then press the Print Button.
This should clear the H4 code and the machine should operate normally.
If not and the H4 comes back then you have either a thermal fuse or heater lamp failure.
Good Luck