Jotul 3 Classic burner going out

[S Stephens]

First time to forum to post....looking for some insight. I have a Jotul 3 classic DV, NG at my camp- works great and I love it. I found a identical one that was a floor model at a local stove shop a Jotul 3 classic NG, Direct Vent stove and had it installed in the spring at my house.
Last month it started blowing the burner out (and pilot) when turned on. Stover fires up just fine and within about 1 minute it blows itself out. This only happens when it starts getting cold outside (mercury drops below 25 degrees) When it is warmer than around 25 it works fine. Also noticed when it starts this behavior if I open the front door a bit the burner will stay on and burn fine. (obviously don't want to do this but was trying some different things to see what the issue was).
Tried with no success to get the shop that installed for me back to get this rectified with no luck. Decided I was going to try to fix myself but need some insight from the experts on the forum here. I believe I have a venting problem but not sure where to start. Venting appears fine as per the manual. Any help would be appreciated.. Thanks in advance for your time.

 

[DAKSY]

Definitely sounds like a venting problem. Is the glass getting blackened with soot as well? If it is, you may have a section of vent pipe that is not completely attached. If you have a horizontal termination cap, take a look at the section in the wall thimble where the "slip" is. Look to make sure that "slip" is fully engaged with the adjacent piece. I've seen where the inner (exhaust) pipe was marginally inserted in the adjacent section & because of this, the unit was sucking exhaust back into the the firebox with the intake air....
Also check your cap for ice dams. Sometimes the exhaust will melt the snow on the eaves above it & if the unit shuts down, that melt will refreeze on the cap & block the intake. Let us know how you make out.