If you have tested the water heater element without a multimeter, and it appears to be working correctly, you should still look out for other signs of wear and tear which could indicate that replacement is necessary. These can include noises coming from the unit, such as buzzing or humming; discoloration of the metal elements; or sediment build-up in the tank. If you notice any of these signs, it is best to call a professional plumber or electrician to assess if a replacement is required.