20+ year old front loader.

Starts just fine with a new igniter, but after a few minutes igniter lights up, but flame does not start. The coils were replaced approx a year ago. Verified gas flow is good, and exit duct clean of lint. Ohmed out the temperature switch by the flame and it appears Ok relative to schematics.

Any suggestions? Could it be a 'new' deffective coil assembly?