Thanks for the suggestions. I guess if nothing else works I probably should have the pressure checked. It's natural gas, and the supply is a 3/4". Even though it's worked okay for 16 or so years, who knows, maybe something happened to the line, or gunk build up on the valves.
My other gas appliances seem okay but they're not as "hungry" (a gas furnace and a gas cooktop). At first I did wonder if my utility provider was having issues, so I cranked all 5 burners on the cooktop and it seemed fine, but I know the tankless can consume a lot more than that. Still, I'd expect some type of ignition to happen...
I did clean the flame rods and ignitor rods when I was cleaning the burner assembly (with some "wire cloth" I use to clean copper pipe before soldering, and also some fine grit sandpaper).
Fortunately the igniter is sparking really well. I can see it pretty clear through the observation window. It'll spark for a couple seconds, pause, and then a couple more seconds. I don't know for sure but I have a feeling that's standard, for it to spark and see if the flame rods detect the heat, then it'll try again for a few more seconds before stopping and throwing the error code.
When I was using my air blower, it's a high volume, low pressure type thing and was great for getting out most of the stuff, and then on my 2nd cleaning when I used the air compressor, I do think the concentrated air helped get more out. But I was only using 50 PSI (I think I had the compressor set there from last time I blew the water out of my RV). I can sure try cranking it up.
Since I'm getting good spark but no flame (when it throws the error) I think that does point towards it being gas flow related. It's an outdoor model so the intake is just direct from the front of the enclosure. I did also make sure the intake grill on the front wasn't clogged (it was fine), and during my troubleshooting I've left the cover off so I know there's no issue with air getting in, and it would still throw the error now and then.
Oh, fan seems to be working good. Using the maintenance mode options, it said the fan was spinning at 3200-3300 RPM. I don't remember what a normal range would be, but it seems reasonable (and seems as loud as it's always been)
I'm going to give it a couple more days and keep track of how many times it fails to burn... it has been so much better recently so who knows, maybe something finally unjammed itself. But if it does come back, I may as well take that burner back out and give it 125 PSI through everything.
Should I be careful blowing that much pressure into the outlet of the gas valve? No risk of blowing a seal or gasket inside there? (I have been careful not to damage or lose the o-rings on the gas feed tubes)
Am I right in assuming on this type of model, with 3 stage heating (3 burner sections) that it'll light up more sections if the GPM flow rate needs it? I understand there's also the PGFR that'll change that flow rate based on demand, so I guess I was just thinking that, if anything, this would point to a problem with either the main valve itself, or the solenoid controlling the primary burner section? Maybe the PFGR could be a suspect, I'm just not sure how those all interact with each other.
Like... does the main valve get the signal to open, then one, two or all three of the burner valves, and the PGFR is just responsible for opening the main valve a certain amount? That didn't quite make sense, because the main valve, along with the other 3, will all get 104'ish volts (when working, and wide open flow rate), so I'm assuming those are just on/off. Is the PGFR yet another valve in front of the main one that can vary the aperture? Maybe because it's variable, it isn't capable of fully closing, thus the need for the main valve itself. I suppose that makes sense. The other solenoids have to be fast acting, on/off, and reliable. The proportional part of the PGFR doesn't have to be as fast acting (and it does use lower voltages) so it might use a slower acting ball valve or somthing similar. But could that get stuck in some unknown state, so when demand is high (all 3 burner sections need to light), the PGFR isn't all the way open like it should be? Just spitballing ideas...
