An iron that will not melt solder is nearly always a dirty or oxidised tip, and cleaning it takes a couple of minutes.
While the iron is hot, wipe the tip on brass wool or a damp sponge, then re-tin it straight away with a little fresh solder so the surface stays bright. This short video shows the method.
If the tip has gone black rather than dull, the article What should I do if my soldering iron tip turns black and stops melting solder? goes into more detail.
If the iron still will not heat, or still will not melt solder after cleaning, record a brief video while you attempt to solder one of the components and send it to us here, or by email to [email protected] along with your order number. If the iron turns out to be faulty, we will replace it free of charge. If it has been damaged in use, we can still send a replacement, and we will quote the price before anything is charged.