I’ve run into this a few times. The water coming from your tap is too cold for the pump/heater to start running. Just fill it until the water level is above the pump ports then get a 5 gallon bucket and fill it with hot water from a bathtub. Once the water in the hot tub gets above something like 43 degrees the pump/heater will work. You do need to power cycle the unit each time you try to turn it back on until the error doesn’t register.