Over the weekend I was driving and the serpentine belt broke unbeknownst to me. When this happened i lost heat, power steering, and the alternator. I continued to drive without for several miles. I replaced the belt and when I did the car continued to have no heat. initial thought was the thermostat was stuck or burnt up from not having circulation. When I started driving the temperature gauge shot all the way up to high. Jump ahead to having it in a garage and working on it, the thermostat seemed to work fine after driving it a bit, the heat turned on and the temperature gauge ran normal. Now whenever I start it in order to get heat I have to rev the engine for a few seconds for heat to turn on. Today when I started it I revved it and got heat but as soon as I stopped the heat gradually went away. Could this be a thermostat issue or is it something more serious like a water pump or a head gasket?