You didn't mention the triac you are using, but my idea is that you have some inductive load and no snubber accross triac.

Consult the data sheet of MOC devices. Motorola has suggested a nice application circuit with snubber.

Try it,

Good Luck

IA

Rauf: 3 ohm 5W will quickly blow with 2A current, and semiconductors burn much more quickly than resistors