The switch on the wall is for the Water heater in LP Gas Mode. When you turn the switch on , you should here the water heater come on. If it does not ignite within 5 seconds, the reset light comes on.I would just tighten the connection to the sink. They just get loose from time to time.
P>S. There is a toggle switch for the water heater in the back of it. In my case I have to remove a drawer behind the toilet,to get to it. The heater will operate in electric mode, if it is on.