Siemens SIMATIC S7-400 Manual page 28

Structure of a CPU 41x
2.6 Cold start / Warm restart / Hot restart
Operating Sequence at Hot Restart
1. Select the startup type "hot restart" on the PG
Operating Sequence at Cold Start
A manual cold restart can only be triggered on the programming device.
2-16
The button is active only if this type of startup is possible on the specific CPU.
S7-400 Automation System, CPU Specifications
Manual, 10/2006, 6ES7498-8AA04-8BA0