i ran into a similar problem ~10 years ago -- thankfully the dude from Sundance was able to fix it the first time by replacing the thermopile. Worked fine for a couple of years... ran into a problem with the gas turning off intermittently... baffled me for a while.... One day when it cut out, I was wiggling the light switch on the wall that controls the flame and it magically came back on! Pulled the plate and inspected the switch --- yep, cheap light switch housing was cracked and would wiggle... simple $1 fix once it was finally diagnosed. I'm sure any tech would have been replacing parts left and right just racking up $$$....

I've been meaning to put a thermostat in line with the switch to keep from roasting out the tv room.... still haven't gotten around to that either.

I've had to replace the fan twice now -- original lost the bearings and started squealing, second one lasted ~7 years before it started rattling really bad --- last one has been running great so far..... If anyone is looking for a replacement fan, this is where I got my last one... best price I cold find at the time...
http://www.fireplaceblowersonline.com/

Pro tip --- most of the fans use the adhesive backed velcro tape to hold the fans in place.... that works... for a while until the adhesive gives out and it rattles like hell - sometimes it rattles like hell anyways.... I decided to get creative -- had some killer magnets lying around and realized they were more than strong enough to hold the blower in place - 3 across the bottom and 3 across the back. Thing doesn't budge at all and no rattling whatsoever. I even got more creative and cut a couple of pieces of sheet metal flashing to shroud the fan for improved air flow (held in place with magnets again) --- now the fire/fan work the way it is supposed to instead of the half assed way it did.

Dude, you'd be surprised how many questions are answered by PV=nRT. Anything that seems peculiar, does PV=nRT answer that? Usually, yes it does.

THAT is exactly why I wrote that.

If you've got to call for fireplace repair, Wallace's is my pick. I had that dude out 2 or 3 times trying to figure out why our stove was having issues, didn't get charged for anything (it was under warranty). Even if it weren't, I'd trust they'd figure it out and make any follow on calls right if they dorked it up.