Chain jumping off Giant CRX City

[sevieri]

G'day,
I've done about 1000Kms on my CRX City (nexus hub) and the chain has jumped off twice in the past week (first time was a pretty painful experience).
Im not a big fan of paying more to get my bike serviced than i pay for my car so i wanted to know if i could fix before taking to the store.
Had a look at the chain yesterday and it appears to have stretched (?) as it now has lots of slack and can be removed from the cassette by hand.
Anyways any help or pointers would be great.
Cheers

[nfmisso]

Are you sure that rear wheel has not moved forward? Make sure that the rear wheel is pushed back, and the nuts or Q/R is tight.

Chain stretch in 1000-2000km is not likely; unless you are incredibly strong and heavy.

[AndrewB]

Or a cheap chain.

You'll see some links above your question that'll help - "How to check for chain wear". You can use a US ruler or do some conversions if you or a buddy doesn't have a chain wear tool.