Obstructed air intake vent pipes in a direct vent two-pipe system will cause serious combustion problems in a condensing furnace.
- Check to see if the furnace combustion problem is caused by an obstructed air supply pipe by removing the burner compartment cover which will provide free air flow to combustion chamber. If combustion improves then the dedicated combustion air supply vent pipe may be obstructed.
- Check for obstructions in the air intake vent pipe such as nests or leaves. If necessary, clean out with a plumbers tool known as a sink auger.