On Thu, 8 Sep 2016 10:08:04 -0400, Ralph Mowery
wrote:

Have you checked the voltage at the coils ? No more than you are using
that oven it seems there may be something more than just the coils going
on.

The line voltage is in the range 240-242, the coils are embossed 240V.

I have had very little experiance with the lead free solder, but as it
melts at a higher temperature it would seem to me that it should be
beter for the simple joints as far as the thermal cycling.

In my relatively limited lead-free solder experience (just the service
bench - where I always use leaded solder for rework) the joints seem
to develop a dry crystalline characteristic over time when in
situations subjected to thermal cycling. IMHO it isn't a melting
point issue but an alloy characteristic.