We have an HX5 water tower. I was looking through the manual, and I am guessing maybe the steam sensor is broken? Or some other electronic. I'd be surprised if it was scale build up since we have only been using the tower for 4 months, and all the water going through is pretty substantially filtered.
1. How old is the unit?
2. What is your set temp?
3. What is the temp of water you are actually getting (measured with properly calibrated thermometer)?
4. Does that temperature change when you hear and see the strange behavior?
5. Does the unit otherwise appear to be operating normally when it does this?
6. Have you noticed anything else unusual about the unit?
7. What are you using for water conditioning?