Not all lockouts are the same, and the pattern narrows the diagnosis before anyone travels. Locks out immediately on a call for heat — the burner never really fires — points at ignition: electrodes, transformer, or a fuel supply that is not arriving at all. Runs for a minute or two, then locks out points at flame proving: the cad cell is not seeing a stable flame, which means nozzle spray, air adjustment, or fuel starvation mid-run. Runs fine, then dies in cold snaps points outside the burner: fuel waxing, an exposed tank line, or a filter choking on tank sludge that thickens when it is cold.
Report the pattern on the call — "fires then locks out after about a minute" — plus the tank gauge reading and the last service date. Those three facts let the triage distinguish a maintenance-debt lockout from a genuine component failure.