I saw some white powder in my trane air forced gas furnace wondering what's the cause and how to repair this problem,the furnace otherwise works perfectly.

Where is the powder? Finding some powder around the flame bonnet, older models, is fairly common. Sometimes, water leaks from the a coil pan and evaporates leaving calcium salt residue.

Where is the powder? Finding some powder around the flame bonnet, older models, is fairly common. Sometimes, water leaks from the a coil pan and evaporates leaving calcium salt residue.
Ok thanks a lot ,that helps me. So long as there is nothing dangerousely wrong with it.

Trane has one of the best furnaces out there. I have been an HVAC mechanic for about 35 years and if the white powder is around the flue pipe it is most likely dried residue from condensation which is water mixed with acids formed when the gas is burning. This mixture reacts with the zinc in the flue pipe which is on the pipe because when there is something to cause such a reaction you want the reaction to take place with the zinc and not the steel. Zinc is used as a sacrificial substance because it is more reactive than steel, copper, or aluminum. In fact, there is a new product on the market to prevent corrosion to the AC coils that is a zinc "egg" with a hole through the center and cut in half in order to clamp it on the larger freon line. Electrolysis causes reactions, or corrosion when two or more metals are joined. The most reactive metal corrodes. Zinc is more reactive than aluminum, steel, or copper, in that order, so the zinc corrodes while the other metals are unharmed. Only when all of the zinc has corroded will the steel or other metals start corroding. So, what you see is natural and means things are working as they should. DrTom4444

Trane has one of the best furnaces out there. I have been an HVAC mechanic for about 35 years and if the white powder is around the flue pipe it is most likely dried residue from condensation which is water mixed with acids formed when the gas is burning. This mixture reacts with the zinc in the flue pipe which is on the pipe because when there is something to cause such a reaction you want the reaction to take place with the zinc and not the steel. Zinc is used as a sacrificial substance because it is more reactive than steel, copper, or aluminum. In fact, there is a new product on the market to prevent corrosion to the AC coils that is a zinc "egg" with a hole through the center and cut in half in order to clamp it on the larger freon line. Electrolysis causes reactions, or corrosion when two or more metals are joined. The most reactive metal corrodes. Zinc is more reactive than aluminum, steel, or copper, in that order, so the zinc corrodes while the other metals are unharmed. Only when all of the zinc has corroded will the steel or other metals start corroding. So, what you see is natural and means things are working as they should. DrTom4444

Thanks a lot for such a detailed professional answer I guess I have nothing to worry about now as far as the furnace,thanks again.Ethon

I am glad I could help you. Make sure you have the coils cleaned along with the blower fan at least once per year. Oil all motors, also. It only tales 1/16" of dirt buildup on blower fan to kill 30% of the efficiency of the unit. Dirt and mold get in the coils and drain pan. They have to be washed out with chemicals and a pressure washer or high pressure water, depending on how dirty the coils are. A HEPA filter will help keep everything clean, however. DrTom4444

I am glad I could help you. Make sure you have the coils cleaned along with the blower fan at least once per year. Oil all motors, also. It only tales 1/16" of dirt buildup on blower fan to kill 30% of the efficiency of the unit. Dirt and mold get in the coils and drain pan. They have to be washed out with chemicals and a pressure washer or high pressure water, depending on how dirty the coils are. A HEPA filter will help keep everything clean, however. DrTom4444

OK thanks,I think I will have a service tech to come and clean it thoroughly.