Hard-water deposits can contribute to residue and performance changes, but filters, spray arms, pumps, inlet systems, heaters and controls can also cause similar symptoms.
Maintenance
Follow the manufacturer manual for filter cleaning, approved descaling and detergent/rinse-aid settings appropriate to your water conditions.
Professional diagnosis
If the dishwasher does not drain, does not heat, leaks, trips electricity or repeatedly shows errors, arrange a qualified inspection rather than dismantling electrical or heating components.