I have replaced both the thermostat and the thermistor. The heater is still not coming on. It goes through the normal on sequence then displays the correct water temp of 84, while the Service Heater red light remains on. There is no sign of the fan coming on or the ignition firing. The gas valve is turned on and the heater temp is set to 104. There are no error codes. I have cleared all baskets and flushed and recharged the filter. Any ideas? Thanks in advance.