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IF IMPROPERLY INSTALLED, A HAZARDOUS CONDITION, SUCH AS AN EXPLOSION OR CARBON MONOXIDE POISONING, COULD RESULT. 8 VENT DAMPER OPERATION For safe, efficient operation, the vent damper and all flue-product-carrying areas of the appliance must be checked annually, with particular attention given to deterioration from corrosion or other sources. Check vent damper operation as follows: 1. When the boiler is off, check that the vent damper position indicator points to the closed position, below. DAMP