Hi guys I have a hayward 300fdn natural gas heater about 5 years old. I had it running fine. This morning it was still running, the pool was at 87 degrees. But when I checked it this afternoon it had stopped. The service light is on and in the display it is showing the number 56. As if 56 degrees. It will not change mode at all it is stuck in pool mode. I tried restarting it, I unplugged it for about ten minutes and restarted it and it is still stuck on the pool mode and 56. The only thing when I first restart it , it will flash and display the degrees of water temp at 86 and the stops and service light and 56. Any help would be greatly appreciated thanks.