1998 416C IT Backhoe block heater seems to be intermittent

It's -30C hear and it turns over but didn't fire up. I had it plugged in but the block heater didn't work. This has happened before and then it worked after that. I have tried different electrical cords, so I don't think its that. Has anyone had any experience with these?

1998 416C IT Backhoe block heater seems to be intermittent