Gas ovens allow gas to pass through a valve to heat the heating element to the proper temperature. You can control the temperature using the controls on the oven. In most cases, gas ovens cook food efficiently. However, if the ignitor or other parts of the gas flow system break down, the gas doesn't flow properly and the oven takes a long time to heat up or doesn't heat at all.
The ignitor controls the flow of gas to your stove. Thus, if the ignitor doesn't work properly, the gas valve won't open and gas won't flow through your oven. If your oven isn't heating or takes a long time to heat, your ignitor might be burned out; replacing it should solve the problem. If the ignitor isn't the only problem, the oven may continue to take a long time to heat up.
The thermostat often controls how long the gas valve remains open after the ignitor sparks. When the oven reaches the proper temperature, the thermostat shuts the gas valve so the oven doesn't get too hot. If the thermostat is faulty, however, the oven may not heat properly or may take a longer time to heat. Many thermostats are electronic, even in gas ovens, and can be reset.
Gas Safety Valve
A faulty gas safety valve can also create problems with heating your oven. If the valve sticks or otherwise doesn't open and close properly, your oven may take a long time to heat up and may get too hot. If you have a leaky valve, you may smell gas near the oven. If so, turn off the oven and call your gas company right away.
Always unplug the stove and disconnect the gas line before working on it. Many gas oven manuals explain how to troubleshoot and fix problems with the ignitor and other parts of the gas system. However, if you aren't comfortable with the process of disconnecting the stove from the gas line or replacing stove parts, contact a technician who is trained to safely service gas ovens.