Safety capacitor identification

[punkieys17]

Could anyone tell me the size of this safety capacitor. Its across the input of a heating controller. Everything measures ok - it just seems to have exploded and shorted the external fuse. No other markings. Can find the 565-1Y but the 1nM is throwing me. Sorry for asking such a dumb question but I grew up with pin through the hole and uF etc.

[Shonky]

1nF
Y Class
250V
M = 20% tolerance

[wraper]

It does not like there is anything wrong with this capacitor and something else let out magic smoke nearby it.

[punkieys17]

Thank you. The tell tale was the black burn mark behind it - nothing else in the area and the back blown off. It feeds live/neutral into a discrete component bridge rectifier which checks out and there is good resistance between live and neutral as connected to the circuit. Not sure what would cause such a failure - it was sitting leant over above the tracks so wonder if it just shorted somehow. Many thanks for your help.