Have had similar issues and finally talked to Truma rep to get it solved. He had me make sure the unit was turned on all 3 places (on the unit, Firefly, and knob under sink). Then he had me turn the knob under sink off, then back on and then i got the LED and the system started working.
He also told me to be careful not to turn the knob to the clean mode unless that is what you intend to do. if you do that, you will need to turn it back to the comfort setting and run water for approximately 20 minutes so that it will finish the cleaning cycle.
Hope this helps!