Originally Posted by Al and Missy
I can’t explain the pump only aspect, but there is supposed to be an air cushion in the top of the water heater. I can’t remember the exact procedure to restore it, but if you disconnect from city water, turn off the pump, and pull the drain plug on the heater until it empties that should do it. Then replace the plug, hook up to city water and open a hot water faucet until the tank fills and water comes out of the faucet.
The manual for your heater should have the exact procedure.
Here is the procedure in my Atwood Manual for restoring the air gap using the pressure relief valve:
"TO REPLACE THE AIR GAP FOLLOW THESE STEPS:
1. Turn off main water supply (the pump or water hook up source).
2. Let water cool or let run until cool.
3. Open the hot water faucet closest to the water heater.
4. Pull handle of pressure temperature relief valve straight out and
allow water to flow until it stops.
5. Allow pressure temperature relief valve to snap shut; close faucet;
turn on water supply.
6. Turn on water heater and test."
The manual also suggests using the pressure relief valve when draining the tank for winterization.