I can almost guarentee that this is your problem. If you have not heat, that means that the water isn't circulating or you would. The water pump doesn't have to make any noise as long as the bearing doesn't go bad. (I am assuming it has one somewhere.) The impeller is plastic and it just rips apart and the pump freewheels but only the shaft (or whatever you call it) inside is spinning and isn't contacting anything so you wouldn't hear anything. Have that checked or replace it and that should fix your problem, I hope you didn't let it get too hot. Good luck.
