What's your take on this?

My attic mounted Carrier central heating system was new as of 2005. Its a heat only system no A/C. The "fan" only function is not connected but otherwise the system usually works perfectly. However sometimes the heater and blower will not come on regardless of what I try. The wall thermostat checks good and the jumpered Red and White wires at wall will Not turn system on so problem has to be at unit I would think. Example: This morning room temperature dropped below thermostat set tempreture. Thermostat clicked on but unit did not come on. Then about an hour later the unit came on all by itself and worked fine. And this happens every once in a while. My guess is that one of the relays and/or switches at the unit is sensitive and may be starting to fail and/or intermittent. Question: In your experience what is the cause(s) of this intermittentence? Thank you Jerry

[this message was edited by Heaterboy on Fri 7 Nov 16:28]