Wally Bestgen wrote:

Ultimately the only change I have to the system is to add a current fault detector that measures the resistance of the vent solenoid. In the event the solenoid fails and the resistance drops to "0" an annunciator light is illuminunated.

The the "0 resistance" detector is a fuse/breaker.  The resistance falling to 0 is a lot less likely than the resistance going to infinity (open circuit).  I suspect that is what your new device is actually detecting.

However, in the best case, such a system only detects that the coil still has the right resistance and is being energized.  It does not detect the position of the plunger or the state of the vent opening, both of which can be different than expected due to a number of potential failures.  Be careful that you do not get lulled into a false sense of security with such a system -- all it is detecting is the state of the coil, NOT the state of the vent.

Regards,

Hamid