We have the 5L diesel heater on Wanderer. It wasn't working when we bought the boat, and I had it checked when we were in Jamestown last August. The tech right away found it was the PCB that was the problem, "corrosion". He replaced it and Voila! it worked! He told me to run the heater once a month to keep it dry.
What I really liked about this unit, is that when it's raining and the boat is closed up, we can turn on the "ventilation" mode where only the fan runs but no diesel is burned. It brings in outside air and keeps the boat cooler. Also, when it's cold, it takes outside air with low humidity, heats it, lowering the relative humidity even more resulting in less humidity problems in the winter.
Now ten months later we're back to it doesn't work and it has the same symptoms. It seems the PCB is again corroded. The PCB runs $250. Has anyone else had this problem? Is the unit not made for marine service? Most of the videos I've seen for repair advice are related to van installations. I plan to hit liberally with some Corrosion-X but not sure that's a solution.