Customer had no heat in home, went to boiler to find primary control tripped, tried resetting but boiler did not fire, pulled nozzle assembly and cleaned burner head, put back together, bled oil line and noticed sludge coming out of line, pulled filter and strainer and they were completely blocked in sludge, changed filter nozzle and strainer and re bled oil line, boiler fired with strong flame, let run until boiler got up to temperature, boiler does need to be serviced last servicing on unit on tape was 2018. System operational and working.