Furnace wont light. have replaced heat rod and

furnace wont light. have replaced heat rod and ignitor gets hot. tries 3 times and then only code that appears is lockout. no other codes to help troubleshoot. have checked exhaust. exhaust blower working and have made sure it is clear. also new ignitor. repair man came and got it working but didn't know what he did and only worked 1 day for $90. Mom is 77 and needs heat and can't afford this again. I fixed my York furnace last year, but it gave code that told me what was wrong. Furnace is a york about 12 yrs old