Dipole keeps melting?



I've got a multi-band inverted V trap dipole antenna which as my first HF
antenna seems to working fine, I like the fact that can get away without a
tuner on most bands.



However I've just started getting into 80meters and the tip of the dipole
keeps melting the guy rope isolator hence the dipole leg falls to the
ground, only running 200watts, the antenna is rated for 1kw.



Everyone suggested its high SWR but not according to 3 different SWR meters
(1.1:5) I always use a tuner built into the amp to give the perfect VSWR but
after 10 seconds the melting starts and the VSWR starts to increase..



Any ideas?