why does my boiler cut off when overheated?

would'nt you stop if too hot. boilers have an overheat sensor, so overheat stops. otherwise Bang, and it only goes Bang once.
Overheating, would tend to suggest that pump not working, or not working fully, could be a build up of scale or anything. Get it seen to before it goes bang. once it goes bang, new boiler, cheaper to repair usually!

SD
January 2013