I have a Rheem 04EAUSR and when I turn it on and set it to call for heat, the unit starts up and blows air, but it's not hot. When I went to the garage to look at it, the flame wasn't on. I went through the quick check guide on under the panel and after following the steps I've found out that my igniter doesn't glow at all. What is the next step I should take to diagnose the problem?