Oven problems are fairly simple to diagnose.
The most common complaints are:
- The pilot won’t stay lit.
- The oven won’t get up to temperature.
- The oven gets too hot.
- The oven does not cook evenly.
Problem number one is probably the most common. Usually it’s the thermocouple that causes this problem. When lighting the pilot, if the thermocouple is not directly in the flame it can not get hot enough to allow it to open the safety valve. If it is directly in the flame and it won’t stay lit then the thermocouple is probably defective and needs to be replaced, Keep in mind that some safety valves have the thermocouple permanently attached so the entire valve must be replaced.
If you’ve replaced the thermocouple and attempt to light the pilot and it still will not stay lit then the safety valve is defective. Remember to check the type of safety valve you have to get the correct replacement. For correct identification procedures check out this Tech Talk post.
When working on any type of gas equipment always remember to shut off the gas!
Number two is usually a thermostat problem. When you set the thermostat at a set temperature and it does not reach that point it may be one of two problems:
1. The thermostat may be defective.
2. The thermostat may be out of calibration. To check the calibration get a thermometer that you know is accurate. Put it in the oven and set the thermostat to 250º. Open the kick plate below the oven door and watch the burner flame, if it goes off before the oven reaches 250º you may be able to calibrate it.
To calibrate a thermostat remove the knob and check to see what type of thermostat you have. The thermostat is either a type with a round disk that has two screws holding it in place or it will have a D shaft with a small screw in the center of it. In either case only turn the disc or screw a fraction of a turn at a time and no more than a quarter turn either direction.
Continue to turn the disc or screw a fraction of a turn each time until you see the burner come back on. If you reach that quarter of a turn point and the burner does not come back on, the thermostat is defective and must be replaced. If the burner comes back on, watch the temperature of the oven and if it gets to within 5 or 10° of the preset temperature, you are good to go. It may take several tries to get it properly calibrated.
If you still can not get it calibrated within the temperature range, you need to replace the thermostat. All thermostats are preset from the factory and should not require calibration when installed. If you find that the new thermostat does require calibrating, follow the previous instructions.
Number three is also a thermostat problem. Follow the same procedure to calibrate as you did for the oven not getting to temperature. Again, if you can’t get it to calibrate, replace it and the oven should heat to the correct temperature.
Number four is a common problem after a new thermostat has been installed. All the thermostats have a capillary tube with a bulb attached to the end of it. This is the part that senses the temperature in the oven. The bulb is attached to clips inside the oven. If the bulb is not put back in the same place, i.e. it’s just stuck in the oven cavity and left hanging, then the thermostat will run “wild,” meaning the oven cooks unevenly.
Remember to get that bulb back into those clips no matter how hard it may be.
If your oven is running wild check and make sure the bulb is installed properly. Another reason for the oven running wild is that the thermostat is totally defective and in this case must be replaced.