Can a Bad Heat Exchanger Cause a Flame Out in a Gas Furnace?

Furnace Heat Exchangers

• With a traditional home heating and cooling system, the furnace heat exchanger consists of a walled, sheet metal enclosure that sits on top of the furnace burners. The heat exchanger compartment directs toxic gases upward into the furnace's flue chamber. Meanwhile, the exterior surface of the exchanger converts cool air into the warmth that’s blown through the system's ducts. In effect, the walls of the heat exchanger provide the only barrier between toxic flue gases and the air that’s sent through the ducts. When flame outs occur, the furnace burners ignite in an irregular or sporadic manner. Repeated flame outs can eventually damage the heat exchanger's walls.

Heat Exchanger Leaks

• Heat exchanger leaks occur in areas where the exchanger compartment has suffered damage. Damage can appear as rust, cracks, rust perforations and flame marks from burner flame outs. These conditions typically result from old or malfunctioning furnace parts as well as from poor maintenance practices. Malfunctioning furnace parts can result from condensation from air conditioner coils, accumulated dirt or debris, and broken seals or gaskets. Since the exchanger compartment undergoes extreme conditions of heat on a repeated basis during cold weather, the materials that make up the walls can quickly deteriorate when furnace parts function at less than optimal levels.

Burner Flame Outs

• A gas furnace system uses a room thermostat control to regulate the furnace’s operations. Once the home’s temperature falls below a certain pre-set level, the thermostat triggers a sensor that ignites the pilot system and burners. Normal burner operation occurs in a silent, orderly pattern with blue flames appearing after the pilot flame ignites. With a bad heat exchanger, the flame pattern may appear jumpy, sporadic and burn yellow rather than blue. After the burners light, a furnace blower circulates warm air through the heater duct system. With a bad heat exchanger, the furnace blower will cause the color of the burner flames to turn yellow or switch back and forth between yellow and blue.

Causes

• Bad heat exchangers often show signs of thermal expansion caused by overheating conditions within the exchanger compartment. Moist or wet conditions within a basement area can cause condensation effects that appear as rust areas on the walls of the heat exchanger. Further rust deterioration may occur as a result of chlorinated vapors that move through a home’s duct system. Chlorinated vapors come from household cleaning products, detergents and paint thinners. As return air vents send air through the heat exchanger compartment, the mixture of chlorinated vapors and humidity accelerates rust formations on heat exchanger walls. Overheating conditions can also result from dirty air filters blocking air flow through the heat exchanger compartment.