Yes, vinegar can be used, but it is not recommended or preferred because of the amount that would be required to properly descale the heater. Vinegar once exposed to the various minerals dilutes and loses its strength to function rapidly. Therefore, vinegar must be discarded, then reintroduced full strength and the process restarted multiple times over a 60+ minute period of time. Navien (the #1 bestselling manufacturer in North America), has instructed all their certified specialists NOT to use vinegar due to its ineffectiveness. At Earl’s Plumbing we use a product that does not dilute, and this allows us to complete a basic and proper descale (flushing) in only 20-25 minutes. Although this product is more expensive than vinegar, it is far more convenient and thorough, and with less time it allows us to reduce our price to the customer.