When I plug in the AC power code I always check the AC polarity light to making sure it glows green. Yesterday I plugged into shore power and turned on the AC switch. It was fine, glowing green. However, when I turned on the hot water switch at the instrument panel the reversed polarity light went on (red). When I turned off the hot water switch, the polarity was fine again, green. This is the first time this happened. The other switches, battery charger for example did not have this problem. Any ideas?