We own a 2018 Unity with a Truma Tankless Water Heater. The heater works great with the outside cover removed but faults out when the cover is installed. The fault code is seven short and one long on the red LED light with the inside light (LED3) flashing rapidly. The cover looks completely clean. I have checked the cover and fan housing and all looks clean. Does anyone have a suggestion on how to correct the heater?