when you place the house battery switch to "use" it closes the relay to power 12 volt throughout the RV. The water heater's control circuits, and also things like the fridge will use 12V power even if you are cooling using propane.
There are tons of parasites in the RV.
That said, if you have it plugged in, even to a 15 amp circuit, the converter will be powering the 12 volt loads and charging the house battery as needed too.
My guess is that your converter isn't powered up. Could be a breaker or fuse problem...or could be a bad converter I suppose....
Or it could be a bad battery too, just not taking a charge
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