There is a high limit/reset button on the bottom. Often when the rocks are packed to tightly, this will hold the heat inside the unit and not let the heat flow out a away from the unit. This causes the whole heater body to heat up too hot and send a premature hot message to the high limit causing it to trip. Restack the rocks in a way that allows heat to flow up and out and this should stop this problem. Also place some flat rock between the back element up high to reflect some heat away from the sensor for the hi limit which is located at on the back of the heater on the top in the middle inside the piece of rolled sheet metal. That silver tube that leads to the sensor is a fluid filled tube not a wire. You will need a pen or pencil to put inside the hole to reset the hi limit as your finger is too large. There sould be an audible click when it resets. If when you press this hi limit/reset button it is springy (about an 1/8” of springiness) that means it has not tripped and you may have another problem.