Line for Flymo strimmer?,

[clockworks]

Having a nightmare time with a Flymo Powertrim 500XT strimmer. The line breaks every 5 to 10 seconds. Often when the line breaks, it melts inside the drum, making it almost impossible to find the end to feed it back through the guides.
The strimmer is 2 years old, and has been used maybe half a dozen times. The line came with the strimmer.
I'm only cutting grass.

Any recommendations for a decent line that I can buy tomorrow from B&Q?

[clockworks]

I bought some generic 1.6mm line from the local garden centre. Strimmer is working a lot better now.