I have a Nordyne E1EB-15HA heater/furnace. It runs great about 99 percent of the time. Every now and then, I have to switch from heat to off, and then off to heat to get it to kick on. If I switch the fan to 'vent', the fan starts up every time. What is the most likely cause? Is there a sticky relay? Sequencer? Or Limit Switch? What are the sequencers? Are the limit switches limiting the temperature of the coils? I believe the fan has to kick on, and then the coils heat up after the fan is running. Is that a true statement? If so, which relay controls starting up the fan. Any theory of ops or info would be appreciated.

Sequencer more than likely