Temperature does not always reach set point of 425 F.

Oven will not hold correct temperature:------- This can be caused if temperature probe not working.Resistance across temperature probe leads at room temperature (70°F) should be approximately 1096 ohms.----------- Other possibility for this problem is :--- Temperature control not calling for heat.When heat is required, there should be continuity between terminals 6 and 7 on temperature control.-----------Inadequate or improper ventilation.Check ventilation hood. Verify draw and make up air adjustment.-----------If all this checked out ok then its calibration problem.For calibration follow this procedure:--
It can be problem with temperature controller. TEMPERATURE CONTROLLER (Standard-Control Models Only) The calibration of the temperature controller should not be changed until sufficient experience with cooking results has definitely proved that the temperature controller is not maintaining proper oven temperatures. Before any recalibration is attempted, the oven temperature should be checked by the following procedure: 1. Remove all trays and pans from the oven. 2. Place a thermocouple or a reliable mercury oven-type thermometer at the center of the middle rack. 3. Turn the oven ON and set the temperature control knob to 400°F. 4. The amber "heat on" light will go out when the oven temperature is reached. 5. Allow three cycles for the temperature to stabilize. 6. Read the thermocouple or thermometer immediately after the light goes out for the third time, and again immediately after it comes on the next time. 7. If the average of these readings varies by more than 10°F from the dial setting, recalibrate by the following procedure. Recalibration should be attempted only by a competent service technician. Use the following procedure to recalibrate the oven: 1. Loosen the two set screws that secure the temperature-control knob to the temperature-control shaft. 2. Remove the knob from the shaft, being careful not to rotate the knob or shaft. 3. Replace the knob on the shaft so that the indicator mark on the knob points directly at the temperature that was measured at the center of the oven. 4. Re-check the oven calibration. ----------- Part number for temperature probe is 1181996 and you can order if from the Southbend service center. -------- If you want the manual and wiring diagram for your oven.Please click the link directly:-- http://www.retrevo.com/search/v2/jsp/mytrevo/myTrevo.jsp?page=man ----------- after you click the link,a page will open in that you fill the 5 letter number.And click the "download now " option.It will ask you to save or discard.Click the save option and download will start.It will take 2 mins to download.Then click the download file to open it.And go through the manual.------------This will help.Thanks.Helpmech.

There should a suitable atmosphere for oven also .......
so try it some times in hot places...