My furnace turns on, and sometimes, has blow back through the tube leading back to the water heater, causing condensation on top of the water heater, blowing out the pilot light. Then 9 out of 10 times, the furnace vents out properly. I don't understand how this can happen.
The HVAC repair men are stumped also.They replaced the old water heater that was doing the same thing. Then they changed the vent shaft from a "y" to a "t" connection leading to the vent to the roof. It works 9 out of 10 times perfect, then the furnace turns on, and the vent leading back to the water heater gets hot all the way back to the water heater, and the top gets soak and wet, and the pilot goes out. Frustrating as hell. The vent on the roof seems clear as the steam is clearly coming out .