Another thing that could be causing the thread to break is dust bunnies under the needle plate. I am shocked how quickly it builds up. I use the Schemetz HLX5 or the Inspira needles usually # 12 or 14 tension around 4 & I use thread from Connecting Threads. I used to have alot of trouble with the thread breaking but after trying different things I have no more problems.
One other thing is the height of your take-up bar. It should be high enough off the machine bed to be able to slip a couple fingers comfortablby under the bar or your quilt on the bar.