Electric Water Heater Hiss

Good morning all,
I have a new 30 gallon Rheem electric water heater in my condo (July 2007). The geniuses that built the place put them in our kitchens under the sink. My old one blew and flooded my downstairs neighbor in July.

This morning, I was at the sink, and heard a hissing sound coming out of the water heater. I went to the electrical panel and shut the water heater off. The hissing sound stopped.

Ever heard of this before? I don't remember ever hearing hissing coming from the other one.

heater

It can be the noise of water in contact with the heating element "boiling". Or it could be arcing at a loose connection. We cannot tell which.

Possibly the temp and pressure valve is blowing off. It would dump hot water
side of building [by copper pipe ending 6" off ground] or elsewhere.
Call plumber BACK.

Thanks! I'll call them back in.

There could be two reasons for the hiss, assuming it isn't a relief valve opening. The first is that one of the elements (if there are two) has a pinhole in it and may fail soon. The second is that elements are more noisy if not turned in a specific orientation. When replacing the elements, I align the two tubes of the element straight up and down.

I've heard elements that sounded like a 747 on approach. Some elements will hiss for a few minutes and then become quiet as the temperature begins to rise.

From this page:

"Q: I just installed a water heater element and now my heater makes a humming sound.
A: This is called a “harmonic.†If the element is installed so that the loop is horizontal, the vibration from the electric current will cause the element to hum. This noise can be prevented by installing so that the loop is vertical. The flanged elements have arrows on the flange indicating the vertical position of the loop. To eliminate the humming on screw-in elements, tighten the element another half turn. In some instances, less than a half turn will stop the harmonic."