My furnace turns on and blows cold air, and does not actually ignite, have followed instructions on it to turn it off have turned thermostat down and power off to furnace have waited for time for it to clear out, but won't ignite when turned back on still blows cold air, model#RGPJ-05EAUER

Inside the flame is an igniter that glows red and ignites the flame to the gas. On the other side is a temp. sensor . This is grey or black . Remove the retainer screw and clean the sensor with steel wool until its silver. Put back in and my heater stayed on

inside the flame is an igniter that glows red and ignites the flame to the gas. On the other side is a temp. sensor . this is grey or black . remove the retainer screw and clean the sensor with steel wool til its silver. put back in and my heater stayed on

There is no grey or black temp sensor on the otherside. When you say other side what do you mean? Is it possible that there is no flame sensor on a Rheem Criterion gas furnace?

I believe senc is talking about cleaning the flame sensor. However, if the gas never ignites, the flame sensor isn't the issue. Does your unit have hot surface ignition (glow plug) or spark ignition? If you have a glow plug, check for power going to the igniter when it should be glowing. What does the diagnostic light on the control board blink when the unit fails? Oh, and how old is your furnace? IF you can post some pics of the inside of the furnace and controls we can tell you if you have hot surface or spark ignition. It may have nothing to do with the igniter, it may be a pressure switch or limit problem. Let us know exactly what happens when you turn the power off and back on at the furnace (with a call for heat from the stat). The more descriptive you are the better chance we have of helping. Take care.