We had an error on our Truma this AM after changing it from ECO mode to COMFORT mode. The remote was flashing. I checked the external LED and confirmed the message to be the Truma circulation pump not having sufficient water, no prime. We are using our fresh water tank at this campground. It didn’t take long to realize that after I had sanitized the fresh tank, which requires bypassing the Truma, that I hadn’t turned it back on. We hadn’t used any hot water since arriving so hadn’t noticed. We turned the valve to inline and heard the water fill the Truma, but shortly after cycling the outside and remote switches we still flashed in COMFORT mode. I was puzzled for a bit, but the error was the same sssllsll indicating the Truma circulation pump had insufficient water aka prime. I then bled the kitchen hot faucet and had spurts of air and then steady flow. I recycled the outside and remote switches and we were back in business. I believe the Truma didn’t flash in ECO mode because there was water in the unit.