Lobster wrote:
Isn't the blue part of the flame unburnt gas though? I don't follow
that one, as my problem seems to me that for whatever reason I'm not
getting up to temperature quick enough!

The blue is burning gas, just not as hot as the outside of
the cone (if evident). If the gas is not burning properly
you will get a yellow, perhaps evidently smoky, flame. You
said that the torch seems to "give a good blast" so I'm a
little confused as to why it's not heating the joint fast.