Ya, I examined the heat exchanger a couple time and it appears okay although it's showing it's age by turning white. I have also cleaned the flame roll-out sensor as well and it looks great? After it cycles and relights once, it runs fine and cycles okay most times except when it doesn't? Maybe...
I replaced the fan motor last year and had to clean out a clogged vacuum line and replaced high limit sensor last month. The high limit open code is back. The heater will cycle back on, reignite and run after it drops it's flame. My question is this: what are the odds I purchased a defective...