What Scott said is golden knowlege.
On any day where it is close to freezing you should winterize or run a heater to keep it above freezing in your trailer, box truck ect....>If you have a question as to if it is frozen get the machine warm as you can before you rin it. Also if it is freezing and you are shutting it down give the ice an "out" Open the hoses and it can expand out an opening rather than against machine components.
The burst disk did what it is supposed to do. One trick to warm it up is to start it with no gun on it so it will force any small ice crystals out of the system before it has a chance to clog it.