Warming up problem

Question

the words "warming up" on display, it can't reach the ready temperature. I pushed the reset button in the back. it worked for several times for short periods of time but then the problem returns. when I pushed the reset button in the back of the unit, the unit was fine. but only for short period of time. I changed the circuit breaker because at one time the breaker was tripped. the unit still heats food up but slow coz it cannot reach its full temperature so I get a "warming up" "please wait"