Why would the DSI light come on if you are only using Electric, not gas?
Assuming it is an Atwood (And as someone said that now includes Dometic) they use a single pair of thermostats.. You can easily tell if this is the case by opening the outside door. Roughly in the center is a piece of black foam with 4 electrical connectors (may have more wire but 4 connnectors) one pair is marked T-Stat and the other ECO These are used by both Gas and Electric.
The light is properly called a FAULT light, not a DSI and was mislabeled.
Two things will trip it.. ONE. if the burner fails to light (Or the control board fails to SENSE the burner has lit) when on gas.
and 2: On either gas or electric, if the ECO opens (Or you pull the RED wire during winterization like you are supposed to which has the same effect, it connects to the ECO).
Your water may be getting too hot.
How to tell?
Put a Candy or meat thermometer in teh hot water flow. Shoudl be 120, mine is 160. I thnk 190 is FAULT time.
Note that this simple test does NOT void warranty.