Hi, my name is ***** ***** I have been in the home improvement and repair field for 20 years. I will be very glad to help you today. It does not however say that it is immune to power surge. The timer has been damaged by power surge. Possibly a wire at one of the connections will look scorched. If you inspect the wiring you will very likely find evidence of a damaged wire. When you find this it will confirm that the timer will need to be replaced. Unless a wire has simply got a loose connection. Here is a wiring direction to help you investigate.