Recently we have experienced a code 14 ignition lockout (3 tries at lighting) before it locks out. this is because the 4th burner at the end of the manifold does not always ignite
I read all the forums and cleaned the flame sensor, not a lot different. Then I realized for a flame sensor to work it has to have a flame!
The symptom is that the first or second burners closest to the Hot Surface indicator always light immediately when gas comes on but #3 and #4 ports on the manifold, the flame sensor is over #4, sometimes do not light. Consequently the flame sensor doesnt detect flame and after 3 or 4 tries, enters lockout.
I have blown any dust away and cannot determine whether it might be gas valve pressure, dirty burners or something else. One site talked about cleaning burners but I could not find documentation on this, or a service manual online.
The problem is the same with the cover left on or off, so any help would be appreciated. It;s just started acting up the last few weeks randomly.
Most furnaces will have a cross over to allow the gas & flame to connect all the burners. This is usually a open slot in the burners that faces the exchanger openings. Remove the burners and use a thin piece of metal (A thin blade made of a tin can will do) to slid into that slot to clear any debris build up. I you really can't remove the burners you can try bending your home made slot cleaner back on itself to still clean the slots while they are in place.
What ever you do, be mindfull of how fragile the igniter is to the burners being removed or your in place slot cleaning attempts.