My 2005 Sundance Laguna is not heating the water anymore. It has worked flawlessly for 15 years minus some small easy repairs I have done myself. The heating light on the panel lights so I do not think it is the thermostat unless the thermostat can fail and the light still goes on? It is NOT a FLO error. I have replaced the flow switch once and there are no flow issues right now. In fact, right now the panel is not showing any error at all. Do you think it is simply the heater (Sundance part 1-6500-063)? Thanks!