Weil McClain boiler 68 series, costumer let fuel oil tank run to empty. went to check it out bled air from fuel line,changed nozzle & filter. Fired it up it worked fine,boss always wants to run several cycles on everything we work on to make sure everything is working right. Evetything tested good,done smoke test,draft test etc.

Let boiler run for awhile while i was at lunch. Came back and the pressure relief valve had released some water onto the floor. had to replace the relief valve , fire the boiler again and got a puff of smoke when it fired.

The rest of the day the thing would fire perfect and then the next time it would smoke again.Fire good , smoke,smoke,fire good. ???