Your story is such a shame of poor dealer knowledge or support. I'd strongly suggest you to change your servicing company. They are not willing to take any risk to help solve that problem that is critical if we look at the safety of it. Don't wait someone get crushed. If that unit has been bought new and act like that since then. It looks like there is transistor problem in current control. A new controller is not such an expensive test and these control can fail so even if they replace it and it shows that the problem was not that then they just have to keep it. They will have one to try some time or even to sell it when they will need. Unless you are dealing with a very small place that we call "jobbers" there is no way your problem can't be fixed. Been a tech myself and when a tech say that it is just the way it is then sometime it is to cover their lack of aptitude to understand or fix the problem. Can't fix it then tell the customer it is normal. Most of the time the customer will believe because he must trust the pros. Sorry that you have to loose such an incredible amount of time trying to get answer for your product that you surely has paid a good amount of money. Hope you will be satisfied soon.