R23 water heater pump runs after draining

[cstpt]

In winterizing our 2018 R23 for the second year, I encountered something I didn't last year. After draining the fresh water tank, I removed the hoses from the water heater to drain it. As soon as water started to flow from the tank, a pump went on, which seems to be trying to pump from the (empty) fresh water tank into the water heater. I turned off the house power to stop it and let the tank drain completely. When I turn on the house power, the pump starts up again--I can feel puffs of air coming out of the hot water outlet. Reattaching the hoses has no effect--the pump keeps going.

I assume there is some kind of sensor that tells the pump to keep the water heater full, but how do I stop the pump when there is no water supply?

 

[cstpt]

Replying to my own post, the ever-helpful Andrew Custis reminded me I need to turn off the water pump switch after draining the tank and before draining the water heater. Duh!