Rule #1:  every effect needs a cause. 

Then go back through everything to God.
Then God needs a cause.
Otherwise, Rule #1 is fallacious.
Or Rule #1 is incomplete.

Let’s reform Aquinas logic more completely:

1st Premise:  God exists.
2nd Premise:  God does not need a cause.
3rd Premise:  Every effect (except God) needs a cause.

Then all effects chain back to God.
Then the logic stops.
But this chain of logic is a tautology.
You are starting with the premise that you are attempting to prove.
So, you prove nothing.
You are concluding with what you agreed to at the beginning.