One for the Pro's

Customer is faced with a puzzling situation. Looking for suggestions. The unit is a small direct vent set up for propane at ~7500 ft. elevation. Vent is straight up 8 feet through roof. Customer cannot light pilot with the glass in place. If the glass is removed the pilot lights no problem, and will remain lit after glass is secured in place. Once the pilot is lit the stove functions as it should with the glass in place. If burner & pilot turned off, pilot will not light until glass is removed. If the pipe is disconnected from unit pilot will light. Customer feels air moving up pipe when removed from unit (pulling up thru intake and exhaust) confirmed with candle. No reports of sooty flames or problems once the pilot & burner lit. In theory the direct vent should be pressure neutral once the pipe is connected. Customer believes ignitor is working consistently (and certainly not a problem with glass removed). Theories?

Had that very problem early on with the bigger brother to this stove. Vertical venting drafted too well. Incorporated a pilot shield into the burner design and no more issues. That burner design was incorporated into this model from the start. Thanks for the input. The customer has been very helpful but it seems the ignitor may not be as consistent as previously thought. Gonna focus on that first, might be a bad wire.