Why your T12 soldering iron can't melt old solder?

7 Reasons You may not be Able to Melt Old Solder with Your T12  Soldering Iron

　　Problem:Not enough temperature to melt the solder–the soldering iron is too cold.To liquefy most solder types,temperatures must get to around 400°F(204°C).Now,if the iron is not hot enough,it wont have enough heat energy to melt the solder!!!!!

　　Tip oxidation:If T12 soldering iron tip is oxidized,it can fail to transfer heat well.If you leave the iron unused for a long time,oxidation can determine the penetration of an oxide layer on theT12  tip.This coating can be removed by passing a sponge along the tip or polishing it with fine sandpaper.

　　Solder Impurities:The solder may not melt if has impurities or contains excessive lead.Since lead has a higher melting point than tin,solder with high content of lead will necessitate a larger-temp to seep.

　　Not Enough Heat Transfer:T12 soldering iron may not be getting sufficient heat onto the joint.This occurs when the tip of iron is not well-tinned(coated with solder)or when it does not have good contact to the solder joint.A clean and tinned tip also hopefully increases heat transfer.

　　Function of Flux:It removes oxidation and helps in proper flow of solder.Too little flux and the solder may not melt at all.Using flux on the solder joint makes it easier to melt the solder.

　　Regularity or Defectiveness of Solder:The solder itself may not be new,or it may be defective due to improper preparation,which can affect its melting method.This can be fixed by using fresh solder.

　　If there are any problems with your T12 soldering iron,then by fixing them you should be able to enhance the performance of the iron and you will certainly be able to melt old solder without issues.