My oven always starts up fine. If I use it for a long time and vary the cook temperature- all of a sudden it will fail to light and the temp begins to drop. It tries to light about every 5 min. by sending out 4 sparks or clicks. If I turn it off and wait 30 min. it will start working again. Usually I remove the bottom of the oven and use a manual lighter the next time it sends out the clicking sparks. That will work and it usually keeps working that day. If I don't realize it is malfunctioning, the oven begins to smell some like gas where it tried to light, but failed. I can always light it manually or turn it off and wait awhile. It has done this for years. Any suggestions?