The city shut off water for a couple hours overnight without notice. When I tried the faucet in the morning it ran dry. I also noticed that a pump in front of my hot water heater started making noise, almost like water is constantly rushing through. The pump is hot to the touch. It's never been audible before. Turning the pump off overnight (wall switch on the left in the photo) and back on doesn't change much.
I believe some air has gotten into the pump. How do I bleed the air out? Here is a picture of the pump on the cold water line leading into the heater.
The hot water heater is on the 3rd floor. This is in a relatively new construction home, built in the last 5 years. The pump is at the top of the picture.