If, after resetting and getting your water heater to gas light again, your fault lockout occurs again ....the following link might help. Scroll down to Old-Biscuit entry where he suggests that the thermostat for the water heater may be failing.....which should also result in problems even when using the using 110VAC as the heat source.......flaky thermostat may work sometimes and fail others just to make life exciting. Other failure mechanism suggestions are also mentioned in the link.
Water heater in DSI Fault mode - iRV2 Forums
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