Gas soldering iron - Yellow flame only
There is usually a sleeve between gas cylinder and burner, which you can rotate to open a hole : this allows air to pre-mix with the gas for a blue flame, or close for a yellow flame.

I can see it in the linked advert : it opens four holes. Ensure they are open by rotating the sleeve (exercise caution if the sleeve is hot!) The advert calls this part 8 : Guard but does not mention whether or not it can rotate.