Although unusual I did have a TT once that would get a bubble of air in the pump and be a pain to prime. First thing I would try; now that you have the water heater filled from city water; it to fill the fresh water tank really full and let the pump run for awhile. Sometimes this will be enough to work the air out of the system. On the TT I had it was worse then that though. I would have to remove the output line from the pump to force the air out. I hope it's not that bad for you. Check what the other members have said first.
You did rinse and sanitize your tank and system correct? If not don't drink the water and it will smell bad for awhile as the antifreeze works it's way out of the system.