I have found so many poorly done crimps that I have become a believer that proper crimping is a fundamental part of professional fireplace service.
I have spent more hours, than I care to admit, studing crimping tools and connectors. I am now just starting to sort it out. I wish I knew someone to help me get a grasp of it. But I think I have begun to formulate how to address this issue.
I don't think that it is necessary to buy aerospace quality crimping tools, (but if any one industry could justify it, it would be us guys that work on milivolt systems every day).
I do think that you do need a good quality ratcheting crimper. I also have a theroy that the quality of the connector fittings are also a big factor, albeit much lessor of a factor than the crimper itself.
Another thing, I was taught early on that improper wire size can cause excessive milivolt loss in moderate or long runs. I have found this to rarely be an issue. I have seen some drop but found that the wire size was not the biggest contributer, moreover, the drop is a constant that may be able to be disregarded in an intermittent operation problem.
We all know if the pilot gen is strong and there is not enough power back to the valve it is usually switches, (limit, control). I do believe that connectors are also an often overlooked issue. I have rambled on a little but that is my point.