I have a Tempstar condensing furnace that shut down (probably) due to a flame roll out problem.
I found the furnace blower running continuously with no heat.
I discovered that the intake vent had partially melted/burned as well as the PVC A/C condensate drain line and electric air cleaner 120v power cord above the intake vent. See pictures.
http://picasaweb.google.com/lh/photo/21OIIvFAMiXMvHV2XmXC5Oa8BNMmtNzugOlNm-7LitI?feat=directlink

http://picasaweb.google.com/lh/photo/Y327EOJ84Qky2bDGoG4CzOa8BNMmtNzugOlNm-7LitI?feat=directlink

I found the flame roll out sensor tripped (thankfully), I reset it and I tested it with a VOM, tests OK. I also tested the fan limit sensor and pressure sensor (with induction fan running), both test OK (continuity across the terminals).

It concerns me that the intake could get this hot before the furnace shut down! (I had previously seen some heat related distortion in the intake vent but nothing was charred or melted completely through and I had to reset the flame roll out sensor on another occasion, maybe 1 or 2 years ago but no signs of fire damage before.)

I also checked for blockages in the exhaust vent (nothing) and the induction fan drain line (nothing).

I removed the induction fan to check the fan drain and I found a restriction plate that had fallen off the furnace side of the induction fan, it was sitting in the bottom of drain area in the housing where the fan is mounted. (The induction fan was replaced under warranty a few years after the furnace was installed.) The restriction plate snaps in and out so I don't know if it's supposed to be used in my application but it reduces the size of the intake on the fan by quite a bit when installed. Different size = different pressure?
See pictures with and w/o plate installed.
http://picasaweb.google.com/lh/photo/Zagp1bp_8wn98u6ztxtO4ua8BNMmtNzugOlNm-7LitI?feat=directlink

http://picasaweb.google.com/lh/photo/9KKRdlzTuSZBvX5935Q2lea8BNMmtNzugOlNm-7LitI?feat=directlink

Could this throw off the manifold vacuum sensors and cause problems?
My gas valve (Honeywell sv9500m 2674) also has a pressure tube connection to the burner chamber along with the pressure sensor. Is this gas valve affected by changes in pressure or is this just another safety switch just like the pressure sensor safety switch?

I'm really not sure which component is malfunctioning?