First thoughts are are you sure you got all the air out. Second thought, coming from water heater not being completely purged, and maybe bypass valve still in "winterize" position. What happens when you hook it to city water? Of course you may not know yet.
When you turn on the hot water, and it get hot coming out of the faucet, does it stay that way, or does it change from hot, to cold, and back to hot? Another sign bypass valve is wrong. Did you bleed the water heater at the pop off valve outside?
I know, lot of questions, just have to answer then one at a time till you find it.
One last thing, your fresh water tank is full isn't it, and not 1/3 or less on the monitor panael? This may let the pump suck air.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT