"add water" error message.

Question

i just received a preowned A40. i filled the tank and powered on. i thought that i might have to go through the priming procedure but the machine doesn't ask for it. i'm getting an "add water" error message.

customer service says the sensor on the tank may be bad and will ship me a new tank. i'm leary. tank and float/sensor both look fine. i've read that they've had some problems with this product but nothing too specific.

anyone have any history? any one know how the "sensor" works? i hear water sloshing in the heater tank so i think it's primed.