Coleman DGAA090BDTA furnace flame quits after 20 minutes, below thermostat temperature. Fails after 3 auto attempts to reignite. I power cycle unit, still does not ignite. Wait 15 minutes, reignites on first try, burns for 10 minutes, quits. Wait 10-15 minutes, again works fine for 5 to 10 minutes. Repeat. Not really short cycling.
Doesn't matter if filters are on or not, and filters are clean anyway. Cleaned flame sensor. Made no difference. All duct vents are open. Doesn't seem to be limit switches because when I unplug limit switches, fan kicks on. I've read as many DIY sites as possible, several similar questions on this site...watched videos... nothing quite like this.