May Carrier which is 20 YO sometimes lights the first time, most of the time it requires 4 or 5 tries. Draft inducing fan starts first and may run for 60 seconds before it tries to light. Some times it lights after one or two tries. Noticed the system fired up the first time after I shut off the power switch. Some times it gives up then tires again after a five minute delay. Sometimes after it fires up it does not run very long but not always. I have removed some of the return vent covers in case the system was not receiving enough return flow.

Had a service company out and their first response is buy another one. The guy did not seem to know much and kept calling his boss with questions.Do I have a sensor problem? The upstairs thermostat is brand new. Same problem before and after installing the new furnace. Did not have this problem last year and change the filter on a regular basis.

Thanks

Could be a flame sensor problem if so equipped. Clean with sand paper or replace. If a 3 wire pilot you will probably need to clean the orifice or replace if defective.