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.
There are two types of gas thermostats: BJWA and FDO type thermostats. BJWA thermostats are the most common type and older ones can be identified by the nickel sized hole on the front where the knob attaches. (See picture above) However, newer BJWA thermostats may not have that hole. FDO thermostats are usually found on pizza ovens and can be identified by the disc with numbers on it that sits behing the knob stem.