I fixed mine this morning.....it was operator error. I did not have my backflush valve closed all the way and I slowly filled the black tank. As the old saying goes, "always trust your gauges" I know I left home with an empty tank, but it filled slowly after connected to city water. The red light and digital gauge was right.
Light is fixed and the tank is 100% back flushed all in one step.
However that could have been a hazardous experience had we been gone.