The DSI fault "only" means there is LP gas ignition fault. If you have the LP gas function turned on, then it will try and light the gas burner. If it will not light, (this happens for a variety of reasons) then the DSI light will come on. Resetting the fault by turning the LP gas switch off and then on will only reset the fault sensing system and not the physical reason why it faulted. It will then if the LP gas switch is on, try and light again. If the system has a real fault, the the DSI light will come on again and again until the fault issue is solved after it was reset.
The DSI fault has is not part of the "electric" side of the water heater. If you have the electric portion turned on, then the electric will heat the water even if a DSI fault is active.
There is something not totally adding up to the advice given to you to leave the water heater turned on all the time. We need more background on how you are using the camper to tell if that is good advice or not. Leaving the water heater on "all" the time for days and weeks on end will in time create other issues. And a DSI fault is not one of the issues. Tell us how some of this all came about and we can try and help better.
Also tell us what year camper you have and ideally the model number of the water heater. They changed how they work over the years pending year/model.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
Google Custom Search For Sunline Owners Club