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.