Description:
From firmware V4.5, you can conduct an operating system update on an S7-400H system while the system is in operation. This applies to the following S7-400H V4.5 CPUs:

• CPU 412-3H (order number 6ES7412-3HJ14-0AB0)
• CPU 414-4H (order number 6ES7414-4HM14-0AB0)
• CPU 417-4H (order number 6ES7417-4HT14-0AB0)

So you need to go true the dark, however you could get the time as small as possible, when getting the Reserve out of order by setting the RUN/STOP key to STOP. Please consider that there might be NO error-LEDsON before starting with this.

Now update the Reserve and load the software, shutdown the Master on a good way and STOP the Master. ThenSTART the Reserve CPU and look if everything is ok, when everything is ok then start to update the Master CPU with the new Firmware, when not then you are lucky, you have the right Software still in the Master, shutdown the Reserve and put the RUN/STOP switch on STOPand START the Master again and you are again alive with the old Firmware.

Good luck, in about one day you could manage it to update all 16 H-CPUs.