My Rheem Criterion II Heater does not ignite (no fire), even though the whole fan system keeps working. What's wrong? It happened two years ago. A contractor replaced an ignitor. Then it backed to work. Now, it happens again. Is it the same problem? Can I replace the ignitor myself? Where can I buy the parts?
And also, if I don't find the problem immediately, will the gas go to my rooms to kill me? Thanks.

It could be the ignitor. Do you see a glow in the furnace burner area when in the beginning of the cycle when it call for heat?

Gas should not be on to the burners with out ignition. So I do not think it will kill you.

Thanks for your answer hvac1000. And for your question, I do not see any glow in the furnace burner area as usual. So, the problem is still from ignitor? Thanks.

I would bet it is the ignitor since there is no glow. I always hate just to replace parts with out checking them first but the ignitor is not that expensive and may get you fix up. If the ignitor does not fix your problem I suggest you contact a HVAC company to trouble shoot your system. Replacing circuit boards and other expensive parts should be tested first before replacing. NOTE: Do not touch the black or dark grey end of the ignitor with your hand. It will cause damage to the ignitor and will fail again.