I have a solar drainback hot water heating system that is also hooked up to my wood stove. the pump will run like it should, then later I will hear loud noises in the tank and the pipes going to the tank will be very hot. Though the light for the pump is on, it doesn't seem to be running.There is a pressure relief valve on the stove pipes that doesn't seem to work unless I manually pull up on it to relieve the pressure. This then sends water out my overflow pipe and cools the pipes down. Why would the pump only work sometimes and not others? And what do those loud noises mean?