Problems with the glow bar system.....You may even see the orange "glow plug" (called a hot surface igniter) glowing orange and so assume that it's OK. Not necessarily!! You have to measure the current/amp drawn by the igniter and compare it to this repair sheet before you can say it's OK or not. The gas valve has a bi-metal that open when a certain amount of current flows through it to heat it up. The igniter is wired in series with the gas valve. As the igniter gets older or weaker, it's resistance increases to the point where not enough current is flowing to the gas valve bimetal to open it up. As a result, the gas valve never opens up. BTW, a common symptom of the early stages of this problem is erratic temperature control in the oven due to delayed firing of the bake burner while cooking.
The hot surface igniter will not come on - check igniter with a ohm meter, you should have continuity through the glow bar, the glow bar can also crack = new igniter time. The glow bar comes on but the main burner will not light - you should have an amp probe to check properly, but often this is a hot surface igniter problem. The hot surface igniter often looses it's ability to get hot enough to open the gas safety valve. The safety valve can fail, but most times it is just a bad hot surface igniter. The hot surface igniter can also quit part way through cooking , in other words the oven may cycle a couple of times and then it just sits there with the red glow from the igniter. See this service sheet for the proper way and amp readings for the hot surface igniter system. Hot surface igniters do weaken and will eventually generate less heat than they normally could. When this happens they can still allow marginally correct current to flow to the oven gas valve for it to open but not get quite hot enough to ignite the gas burner immediately. When this happens, gas released into the oven can sometimes build up to the point where when finally ignited, the amount of gas lit can cause a small explosion inside the oven or cause an odor of gas with out the oven working. Yes, your glow bar igniter can glow orange-red and still be bad!! How a common gas valve works - click he