Hi Paul, and a warm welcome to the OutdoorKing forum. It's great to have you aboard.
It sounds like you're not having too much luck with the repair centres, so it may be time to take things into your own hands...literally. We all like to learn new things and tinker here.
The problem, being an intermittent one, can be a bit tricky to diagnose, but Bruce may have nailed it right from the outset with an over-heated coil, and that is a good place to start. Without spark it won't run...
Please let us know how you get on there, if that is not the issue, we will start the diagnostic process with you. We will get to the bottom of it, with your help....and give you the self satisfaction that you have done it yourself!
