HI , I have a Beckett fuel furnace that after it warms up to room tempature it will not start again till you bleed it again . Thank for any help

You have air getting into the oil line and that is causing the problem with lost prime.

Low oil level in tank
Loose or leaking fittings or valve.
Bad oil pump shaft seal.
Bad check valve in oil pump.
These are the three main things that cause this.