appliance repairman here?

My gas oven is as dependable as my sisters old Fiat. We put a pot pie in for 90 minutes at 350 and when the timer went off, we pulled it out and the thing was nowhere near done. Checked the hanging thermostat in the oven at it said 225! We've been having low temp/extended baking times for a few months now sort of off and on, literally. I preheated to 350 this morning for 40 minutes and the damn thing got to 225. I checked the igniter (electric) and its glowing like a light bulb but no flame. Could the gas servo be faulty? I turned it off and then turned it back on to 350 and the igniter started to glow and the gas kicked on (does not always do that) and the gas lit as designed. Even shut off at 350 and lit back up at 325 twice in 15 minutes. so whats up? Almost bought a new igniter but mine glows like a filiment, a light yellow. Should it be near white? Temp seems accurate too when it works. Oven is Fridgidaire, 15 years old.