We contacted the dealer and they told us the same thing - no switch on the back of the sink, though. However, we found a switch a few minute later under the far bunk near the fuse box - sure enough, it worked.
I wondered the same thing also - that it may have been something else besides the water heater. But, as herk7769 pointed out, it was indeed the water heater trying to light the pilot. Gladly, we got it figured out and no damage done - whew! Something in the camper must have slid and bumped the switch while we were traveling.
We appreciate all of the help from everyone here. Glad to have some seasoned campers close at hand!
Ben & Autumn
2011 Toyota Highlander
2013 Rockwood 2516G