I'm somewhat familiar with the 3 main rules of injection circuits.

1. At least 6 pipe diameters of straight pipe prior to the "T" fittings.
2. No more than 4 pipe diameters between the "T" fittings.
3. Minimum of 12" drop on the injection loop to create a thermal trap.

My injection circuit follows all of these rules except for one item. The straight pipe prior to the "T" fitting on the low temp return side is too short. The pipe diameter is 1.5" so it should be 9" according to the rule. In reality, it is only 2". All other lengths seem to be correct.

Is this item going to cause major problems or is it acceptable as is? What would be the symptoms if it is causing problems?

I've seen some bizzare piping arrangements that all seemed to function fine. I doubt it will give you fits, but I could be wrong. As a matter of fact, I've even seen it where one leg of the injection loop was piped into a tee turned horizontal (hard to explain, sorry) and it worked fine. Your 12" thermal trap is good piping practice on an injection system that also has a high temp zone, but really isn't necessary otherwise, IMO.