Would a bad timer be responsible for no heat? I know from other sections of your site the answer may also be the Igniter. Which is more likely to be the culprit?
Thanks for any insight.
The most likely culprit would be a bad igniter, flame sensor or gas valve. You can check to make sure that you are getting power to the igniter by accessing the igniter and turn unit on. If the igniter does not glow then you will want to check to make sure that you are getting power to the igniter. Unplug the igniter and check across the terminals for 120 vac with unit running. If there is not 120 vac then then you will need to check from black to ground to make sure that you are getting 120 vac. If you are still not getting 120 vac then the problem would be in the motor switch. If you are getting 120 vac then you would want to check the High limit thermostat and thermal fuse for continuity. If there is no continuity replace the part. If there is continuity on both then the timer would be the issue.