Oil Burner Won't Start After Tank Ran Dry and Refill—Possible Airlock or Water in Line?

The burner most likely won’t start because the fuel system is airlocked after running dry, and/or the fuel filters are clogged, so the pump cannot draw oil from the tank [#5671921][#7533445] Oil-burner pumps usually self-bleed only after running longer, but the control cuts them off when no flame is detected, so you may need to keep the pump running continuously until oil appears in the return/overflow line [#5671921][#5672744] If the supply line is long, the same problem is even more likely; one workaround is to feed the pump from a small tank with the fuel level at or above pump height, then quickly reconnect the line to the main tank [#5672744] Check and clean or replace the fuel filter, including the filter inside the pump housing, and inspect the burner’s photocell/flame sensor after the failed starts and smoky ignition [#5675305][#7533445] One reply also notes that if the burner was run dry, the pump may have seized, so that is another possibility [#5683248]