The H4 code on these machines is almost always a false code. Especially if you have had any power fluctuations or failures.
Here is the text from my tip to solving this problem here on Fixya:
To reset the H3 or H4 condition on just about any Xerox XC or XD series copier press the following key's in sequence and as quickly as possible (with 4 seconds for the first 4 keys)
Press "C" then the far left key (exposure mode) then the "C" key then the far left again.
So in other words C, far left, C, far left
If done correctly the display should go blank.
Now key in 14 as if you were going to make 14 copies.
Now press the
print button.
The machine should reset and the code should be gone.
9 times out of 10 this is a false code that pops up due to
power surges or noise.
If the code comes back this means you have a heater lamp or thermal fuse (more common) failure in the fusing area and will need service.
This procedure will work on all Xerox XD and XC models.