On Saturday, September 10, 2016 at 9:26:40 AM UTC-7, Jeff Liebermann wrote:

...the OP reverse engineered the oven wiring and produced a
schematic of sorts. Generally quite good but a few mistakes. One was
showing an SCR keying the solenoids instead of a Triac. If it were an
SCR, it would rectify the AC going to the solenoids.

A triac can also rectify, if the gate has become insensitive (or
too responsive to noise). If you use the triac to run
an AC relay, and the relay to activate the valve, the valve is immune
to rectification (and if the relay burns up, it's cheap to replace).

Or, just replace the triac on suspicion

Even a small amount of rectification in the triac circuit will walk the
magnetic core toward saturation and remove inductive back-EMF. Next
event: the coil burns up.