Oil heat not running this morning. Cleaned nozzle. While burner was out of furnace I installed the new motor which I had ordered a month ago - the original had noisy bearings. Re-assembled everything and ran furnace. Lights up immediately, runs for 25 secs and then flame goes out. Motor runs until control unit trips out. Bled air from pump and changed cad cell. No difference.:(

You never clean a standard oil nozzle always replace since they are precission devices.

Your unit sounds like it is tripping on the safety control. If the oil flame is being seen correctly IE the cad cell flame detector is working correctly and the flame is being seen then the unit should be running. You might try to put the old cad cell detector back in to see if it works.

If there is good flame,the cad cell is working,and you did not disturb or change any of the wiring the unit should work.

With a muli-meter check your ohms must be below 1500 and stay there it is better if they are below a 1000 put your test lead to f f on the primary and see what you find out.

Check to make sure that the fire chamber is clean so that the exhaust can go up the chimney. Another thing could be that the eye is dirty or not pointed correctly. Hard to tell without seeing in person.