My first post here and a little disclaimer. I am not a certified HVAC technician but more than competent in the field (They all say that right?) Anyway, I've always serviced this myself and generally when this happens (About once every few years) it's the flame rectification probe needing a cleaning. I annually service this, clean the HX, blow out the condensate and ensure it's clear, clean and test both the ignitor and probe, etc. In this last F9 instance I pulled both the igniter and the probe and cleaned them w/ scotchbrite although both looked good and I did get a spark from the ignitor when outside the machine. Gap was good. It was hard for me to see the spark inside as my sight glass isn't great for some reason. Rectification probe current wasn't great but more on that in a sec. So those attempted resolutions didn't help the F09 so I tore it down, removed the burner and cleaned it and also inspected the flame refractor. I noticed it was a bid damp feeling so I took my heat gun to it and removed the moisture and reassembled. It was fine and fired great for a whole day (A joke). I assumed the ignitor was just grounding out on the wet refractor. Not sure why it was damp to be honest as the condensate isn't clogged and I see no indication of a cracked HX (Perhaps you guys can recommend a way to more thoroughly check for a cracked HX?) I have been monitoring the rectifier current and during those F9 times on initial fire I'm seeing a fluctuation of .4 to 3.6 until it fully lights then it's pretty stable 3.9-4.1 uA. I assume this is due to incomplete combustion and a poor flame. I've also noticed a moaning sound (and a slight vibration from the boiler NOT the fan) as of late only on a cold start (Where it has been sitting a bit). And researching this has led me to a potential AFR issue (apparently these things have a tendency to go lean?). I did look at my exhaust pipe and it's never had a hole drilled to check the CO and CO2 readings. I have purchased a gas analyzer to test this and will have it tomorrow. I also purchased a namometer to see what my inlet/outlet pressure is and to ensure i've got no significant drop in pressure during firing (Not likely but curious). That brings me to my questions..
1. In the installation manual for this it tells me the CO and CO2 specs but I see no mention of what my pressure POST regulator should be. The regulator is a 250P-451 Dungs unit and says MAX .50psi (~13.8" WC) but it doesn't say what the actual regulated pressure is so I don't even know what the actual value should be. I know it's a sealed unit and non adjustable but I'd love to know the desired set pressure of this regulator just for my own knowledge. Anyone know it?
2. I've read adjusting the offset can help w/ the low fire AFR issues, is this factual? I see mention of adjusting the off set here but it is mentioning targeting -.02" WC which I don't know what this is in reference to, i'm guessing it may just be gas pressure offset high fire vs. low fire? Anyone care to explain to me what exactly this offset adjustment does? Do it just mess w/ the fueling during low demand (Idle needle on a carb?)? I will also be playing w/ the main needle to check my high fire gas output (They call it a throttle adjuster in the manual).
3. I have read that swirl plate deterioration can cause similar issues but given this is generally on cold fire only I doubt that's the issue. Opinions? If all else fails I will tear it down and inspect it obviously
4. I see no definition of "low fire" and "high fire". I do know how to get into the test mode to control the fan speed so is low fire just minimum fan RPM and high fire max fan RPM? If this is just fan related is there a specific RPM you guys use for high and low fire gas analysis? How far do you guys drill your hole in the exhaust to analyze combustion? Do you guys generally aim for dead center in the spec window or error to the rich side?
Sorry for the basic questions but before I mess w/ any fueling I need to understand everything fully, i don't need to create a bomb here.
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