The taste is likely coming from some kind of mineral deposits on the electric coil inside. These dispensers were not made to come apart and be cleaned, but you could try doing that yourself if you’re handy. As for a professional cleaner, you could probably buy a new hot water dispenser for the same amount (or less) than you’d pay someone to clean it. Sorry to be bearers of bad news. Fortunately, hot water dispensers don’t cost thousands of dollars.