Because of the safety function, I suggest using an off the shelf burner controller such as (12V RV) Fenwal

Safety standards require a flame sense (circuit) to constantly do a self-check. So the excitation voltage will be briefly turned off with an expectation of seeing no flame detected, then the excitation is turned back on, all within a second or two. To see if anything is "stuck".
If you get it wrong, a false positive and leave the gas solenoid on in a flame-out situation, there is an explosion hazard.
I have seen this happen with garbage design flame sense circuits.

I looked at the Fenwal controllers, like all the others they use an igniter and I can't use it the way it is unless I can find out how to isolate the flame sensor circuit because that's all I need. I am lighting the burner manually and just want the solenoid to shut off the gas the flame goes out. The control board that was in the water heater I got the burner from had 3 flame rods, I believe one was the igniter and the other 2 were the flame sensors. They were both connected to the inductor shown below, someone posted that (you could probably do this by having two sets of probes polarized in opposite directions. Subtract one signal from the other and calibrate the difference for flame vs no flame). I believe that's how this one worked. If you have any knowledge of this please let me know. I've seen several other posts of people wanting the same thing (a flame rod sensor circuit by itself without an igniter of fan on a timer.

 

I still believe your better off using that amplifier module.
I haven't any knowledge using that board without having one on hand.
I've been trying to help but you seem to be ignoring my post recently.

 

I still believe your better off using that amplifier module.
I haven't any knowledge using that board without having one on hand.
I've been trying to help but you seem to be ignoring my post recently.

can you make this?

 

can you make this?

I can but that circuit requires 5 volts to activate.
Can we get back to the amplifier module and the readings you measured earlier.
I have other ideas that can work even with a low output from the amplifier.

 

Seayaker,
How exactly was that flame sensor connected to the amplifier module?
Was the metal casing of the burner connected to ground on the amp module?