I have a sip ideal 240 for years.it has a lot of heavy work done mainly structural steel. The big contactor switch inside stopped working last year and a guy replaced it and it worked fine for a few months and then same thing again it will feed wire and gas but won't weld. I switched the wiring over to the other 2 open circuits and it worked for a while. Last week I replaced the contractor switch got a new 25amp 48 volt switch worked for a while stopped again. I rewired it today to the other open circuits and its working again any ideas of what can be causing this have the welder nearly 20 years pretty much trouble free until now. Thanks