I've had the unit for about 8 months, and followed Delta Dude's instructions for pre-heat, and getting chips started. The unit has always performed.
So, recently I moved, and the movers took care of all the heavy stuff...
When I went to use the MES for the first time since the move, I did my normal pre-heat to 270 for 30 minutes, vent open 100%. Unit came up to tempature in the normal amount of time.
Brought temp down to 220.
Add a couple of pecan chips, (I normally get smoke within a couple of minutes), and nothing.... So, I opened up the door, and pulled out the entire chip box. There was some ash in their from previous smokes, so emptied the whole chip box out, and started over. 10 minutes later still nothing.
Opened the door again, and pulled the chip box out, to insure the heating element had not shifted during the move somehow. Looks fine to me... the chips were warm, some had turned dark, but none had ignited. Strange...
I messed with it a few more times, and never got chips to ignite. (It's always been add chips, smoke a couple minutes later)..
If the unit is good, the only other variables involved are the chips and oxygen.
I don't soak chips, just straight from the bag. And these chips are from a bag I've used in many previous smokes.
Oxygen. Before my unit was out in open air (backside about 4 feet from a hot tub).. Now the unit is on a balcony turned with back side about 2 feet from a solid wall
The only saving grace through this ordeal, I was smoking brats and beans.. So, we weren't too put off by the lack of smoky goodness.