Furnace is 12V DC and propane
When t-stat closes the fan will come on to purge combustion chamber then circuit bd will attempt to light off gas via spark electrode
(fan comes up to speed...closes sail switch which allows DC to go to High temp limit switch then to circuit bd)
No propane and circuit bd will shutdown attempts to light off...prevent raw fuel from accumulating
Post brand/model for specific info...DC circuit path
Is it time for YOUR Medication or Mine?
Dodge 3500 w/Tractor Motor & NUWA 5vr
US NAVY---USS Decatur DDG-31