May printer HP4255 always encountered problem of scan failure.

Failure always scan failure. Whenever the technician work on it it works okey. But the problem of scan failure is 3 x a week and cause as money lost and opportunities lost. Can somebody assist ne what part of computer to be clean to removed the dirt that cause the failure. I said this because the technician does not charge us the parts placement whenever they do the troubleshooting . They just clean the system/