Make a soapy solution (1 TBSP dish soap/water in spray bottle)
With the propane valved in for service
Spray the propane line connection at gas valve and check for bubbles
Do NOT spray the outlet side of gas valve ...you will clog up the orifice
IF no leaks on line/fitting ...rinse with clean water
Then using a BBQ lighter see if you can ignite any propane at end of burner tube
Gas valve ----requires both solenoids to open gas valve.
One alone will not open it.
Propane system pressure is only 0.4 psi (11"WC)
12VDC is applied to gas valve solenoids for only 6-8 seconds during ignition cycle....during which time spark electrode is energized
Spark Electrode is also used in 'flame proving' circuit.......milliamp signal generated by FLAME which is detected by circuit board. No Flame signal...No DC to gas valve solenoids (easy to check with voltmeter on gas valve red/black wires)
Gas valve 'could' leak....rare but possible
Circuit Board.....could be faulty (doubt it)
If faulty it is more likely it would NOT send DC to gas valve or not send DC to spark electrode
HVAC guy sounds like a parts changer. Which eventually works if you throw enough parts at it.
Here is the wiring diagrams for 12VDC (propane) and 120VAC (element)
Maybe the HVAC guy can figure it out
