Have had repair guy here 3 times, has got furnace running every time but, quits in few days ? Can use reset 1or 2 times will start , then quits altogether, furnace guy replaced,oil filter,nozzel,checked electrical parts with tester alls good,furnace runs great when it runs? Repair man says maybe pump? Please help were are stumped? Thank you

Do you have an A-coil on top of furnace? It may be clogged up which will cause the furnace to overheat. It sounds like it is not getting enough airflow for some reason. Look at all things that may cause this including the blower. If the belt is loose or the fan blades are dirty it will reduce airflow-in fact, 1/16 inch of dirt on blower fan blades will reduce airflow by 30% which will cause it to fail. DrTom4444