This unit uses flame rectification,
this is a DC signal of micro amps that returns to the ignition module via the modules sense/ burner grnd terminal
. It transmits the weak DC signal to the module to prove a flame exists and is safe to continue operating
. I did not see if the port on the induced draft assembly, where the induced draft proving switch's tubing connects was reamed out good? It will obstruct and cause a wavering pressure thus pop open intermittently which is difficult to spot, I don't trust the flash codes myself, as there are only several possibilities to rectify this situation .
I have a routine I use for these ,
I clean the pilot assembly's mounting brackets surface areas and the burners surface areas touching the pilot assembly mounts, basically we are making a nice conductive path to home, being the burner grnd/sense terminal.
In addition I use 105C degree rated wire and connectors and run a ground wire in addition to the units grounding back to the terminal that is used for sense or burner grnd, usually they are common in the circuit board.
Remember it is only transmitting the faint DC signal that passes through the flame, a flame is a poor conductor and only transmits micro amps DC and that is easily stopped by a patina or moisture or corrosion etc, it does not take much and it is easily disrupted and restored. In fact many times new components seemingly rectify an issue, often the restoration of a ground path for the flame signal is really what fixed everything and if you try the old equipment, it is operative about 40% of the time according to manufacturers. Johnson controls makes a nifty flame simulator ($24)that simulates a nice DC signal that will work on any flame rectification system! it plugs in with the existing flame proving circuit and clamps to ground with a clip, If it wont run with this, no question the boards/module is defective, assuming all limits and safeties are closed, I often bypass them to test with them jumped to see what is going on..jumper clip the pressure switch once it has closed. For the pressure switches I use tattle tales to tell me if any control opens,even if a brief second, that is hard to spot unless gazing at it while it pops opens for 1 second , pressure switches on the threshold will waver and not be evident by watching , tattle tales have a flag that pops up if what it monitors trips or opens. You can by the and pressure switch for what a service call will be alone online and its very easy.Its not worth spending time troubleshooting parts that cost 10 minutes labor as in sensor and pressure switch and any auto reset limits. 1 yr of this is not worth this trouble, unlesss you had a $400 board i would sawp out the pressure switch, sensor limit and module, it wont be much online and if the pressure orifice is not clogged it will run no doubt with the system refurbished. I dont just replace a board and leave old cheap components there to fail next 6 months being a free call back and cutting my profits in 1/2. If a service tech is doing sub $300 service calls much he will be fired, go broke,etc. I had bosses tell me this in the early 90's.