My Trianco EuroStar 70-90 oil boiler keeps cutting in and out. The oil burner keeps running and after approx 8 secs the igniter re-establishes the flame. It has a new nozzle and the oil pipe is clear. I have cleaned the photoresistor. The air setting is 7, could it be lack of oxygen? It has worked OK for two years at this setting. Any suggestions are most welcome.