Lockout due to ignition (AeroFlo furnace)

Have a question. I have an AeroFlo furnace. 3 years old. The ignition lit but the flames wont come on. I can hear the fan and motor running. The ignition lit and shuts off when no flames comes on. After the third time it lit on and no flame comes the system shuts down and I get the 7 red light blink "lockout due to ignition" However, sometimes I shut down the main disconnect and turn it on again and sometimes it start working for a while. after it goes to stand by it wont turn again. What Can I check? I tried using a sand paper on the stick flame sensor but still. Tried blowing the hoses but same. What else can I try or check? Thanks!