If your MUTS relay in the control is not picking when you start the pump motor check terminal 6 on the soft start for 120VAC. If you do not see the expected voltage go to terminal 5. If there is 120VAC at 5 you have a bad up to speed relay on the soft start board. The prints I am looking at shows this circuit on sheet 12 of 24, Motor Control. This is all assuming, as elmcannic said, the soft start is turned on and you have a display.
I repair the most common Seimens 72G problems for the company I work for and majority of the time I've been able to just solder a new relay on the board. With a soldering iron and desoldering tool this can be done easily. Sometimes there is another problem with the board and a relay doesn't fix it.
You can order them from Newark or DigiKey for a few dollars. I can post a picture of the relay on Monday if you would like. The up to speed contact on the soft start stays open until the pump motor is up to speed. While the soft start is inactive you should NOT be able to read voltage(with the power on) on terminal 6 or a low continuity value between 5 & 6 with the power off. It is a NO contact.

Let us know how you make out.

Matt