Simple answer.
1. IF you get 120 on EACH Hot leg to ground or Neutral but NOT 240 between the 2 Hot legs----Either the breaker AT the main breaker box for 1 leg has been moved to the SAME PHASE of the breaker box and that is your problem. OR, like others have mentioned the 2 HOT legs have been jumped. So, easy way to check, is to KILL (turn OFF) the main breaker box breakers. IF you are positive which breakers feed the Oven receptacle turn those ON 1 at a time and read the voltage. If you are NOT positive, then turn on 1 breaker at a time until you get a voltage reading on 1 of the Hot legs. LABEL that breaker. Then turn it OFF. Continue the turning ON breakers until you get Voltage at one of the Hot legs. LABEL that breaker. Hopefully, once you identify the 2 breakers, EACH will power the other hot leg. IF SO, one of those breakers should be on the other phase of the breaker panel to produce 240 at the oven receptacle. Usually on a Main breaker panel on 1 side, every other breaker will be on the same phase.---Eg, breakers 1/3/5/7/9/11 will be on 1 phase and breakers 2/4/6/8/10 will be on the other phase, that is why you see 2 breakers side by side for a Oven/Dryer/AC unit. Even tho the breakers are side by side, they are connecting to the other phase. Doug
