Navian Ch 180 high wind lockout?

Hi,
I installed a Navian Ch 180 combi-boiler for radiant heat in a building 16 months ago. Last winter and even worse, this winter, the boiler goes into lockout with error codes suggesting backwinding in thru the flu.
This is a direct vent system, but it is vented on the west (windy) side of the building. Every time there is high wind-- it locks out.
Looking for suggestions for preventing this high wind flameout/lockout. ? concentric vent ? baffle??

Bob
January 2014