Sharp copier SF-2025 displays an error code H4

H4, not heating up, replace fuser unit complete or work with hivolts and replace an expensive and tricky lamp/thermister . wont be cheap.

. Here use the reset for it first, sometimes power surges can just flip them out but most times will just reappear shortly after reset, indicating the want of a working fuser assembly

Fuser (not fuse) is the hot bit with rollers at paper exit if code fails it needs to be replaced, wont come cheap no matter how you approach it

C-Exposure key-C-Exposure key-14-copy key to clear ... but it will come back I bet...

The cooling fan goes bad and generates false signals. Replace the fan
if everything else checks good. It may also cause intermittent power failures "machine goes dead"

goto sharp service centre and repair it

regards----best of luck