Atwood Furnace

Atwood. as I recall. uses a single wire ignition/sensor system where the spark rod is the flame sensor.

Sparks are about 1000 volts ac... Flame sensor about 1/2 volt DC

A switch protects the chip that detects the half volt (0.480 to be more precise some folks nag on that half is easier to type).

Imagine what happens to that chip when the switch fails to protect (POP goes the detector).

When that happned to me I got a Dinosaur board to replace it .. When I opened the box this trained electronics tech noticed QUALITY... (That's a good thing) and upon a closer inspection I found a part not on the OEM board.. A Gas Discharge Bulb (like a old Neon Night light bulb. in fact might well have been an NE2 (The old neon night light was either an NE2 or NE2H (high brightness).

It was positioned right about where I'd expect the detector chip to be.. A back up protection device perhaps? That board lasted a long time.

Another thing on Dinosaur boards in a separate ground wire on some. This prevents larger current flows from going through circuit board components.
Dinosaurelectronics.com and available on Amazon.
OP: remove the circuit board and lay it out in the sun for a few hours. I know it is wintertime down-under!
Socket should be 1/4 inch US. Think that is 6.5 MM

Ok thanks so far for advice, I will try to find or purchase a 1/4” socket and maybe get circuit boards out , but still think it is more likely to be the sparkler com censor as it dos start and heat for about 5 seconds but could also possibly be board, I will try to get gas valve etc out to inspect and clean first.
Thanks Frank.

Flame sensor probe is the ignitor probe as WA8yxm stated earlier. failure is normally in the circuit board.
Look at your water heater circuit board, It could be same board. If they are switch them and see if it operates.
Amazon Dinosaur circuit board
The circuit board is in the outside access. Normally held in place by wing nut. Loosen wing nut and it should slide out. Contacts could be dirty or corroded. Clean with white pencil eraser. Good idea to coat contacts with electrical de-oxidation grease.

Most unfortunately IMO Atwood was bought out by Dometic…

Has given op on the furnace, to many different things out of stock etc as expensive. Will purchase a new diesel parking heater for less than $150.
Thanks all
Frank p

I have found the majority of my parts on Ebay and Amazon. Dealers don't stock anything! Everything is special order!