Down Draft on Exhaust Vent causing incomplete ignition???
I have 2 80% efficient Gas Furnaces that periodically do not ignite or does not ignite completely causing gas to leak into attic and house. I have had gas company out twice to check for leaks and pressure both are OK. HVAC contractor has been out 3 times, cleaned burners, replaced gas valve on one furnace and now thinks downdrafts from roof vents is preventing furnace from ignighting when it is windy outside. Last time this happened it was very windy can't remember on the other events. This started before Thanksgiving and occurs about once a week. Does the latest explanation make sence with 80% furnace with induced fan ignition? Contractor is recommending replacing roof vent caps.
It does make sense. You may try raising the flue up a few feet also. It would be nice if the tech could see it happening instead of guessing but it does turn out that way sometimes. Could also be something else also.