Ignition problem

I've used the wire in the tie from a loaf of bread to clean various small holes. The one on today's bread measures .016".

you could try putting a relighter on it but i think something is floating around and plugging the orifice.

The Q348U instructions specifically mention for intermittent pilot, nothing about a thermocouple. Besides the igniter rod assembly looks crimped or a press fit in place, I don't think the manufactures intent is a field retrofit to a thermocouple. I will look at it again later.

Since a new gas valve was installed (whether it needed it or not), I believe the present issue is high pressure to the pilot, audible in the video (and the main burner pressure was a bit high also) . I bet the pilot pressure was never adjusted with the new gas valve.

do you have a longer clip of the pilot burner burning? you posted it just as it goes out, we can't see how it is burning before that.

Looks like gas pressure based on your 9.2 mbar would not be too far off 3.5" wc. How long did it stay on with main burner before flaming out? Any obstructions in flue passages in boiler? Draft, chimney clear?

Does it still do that ? Go out with the burner (thermostat) off.

I'm not sure we got an update. I'm loosing track, crushed thermocouple wire, old thermocouples, new thermocouple possibly installed . . .

I'd lower the burner pressure to at least 3.5 WC and adjust the pilot, then reassess the situation.

I have not seen where you actually measured the thermocouple millivolts: open circuit, closed, and dropout. You can use test/ interrupter blocks such as above. Any service call or diagnostic should include gas inlet pressures- everything off in the house static pressure, this pilot only, burner main operator closed circuit, then house under full load. If it does not drop out or drop below the minimum wci PMI, measure manifold pressure PMI and adjust the regulator on the valve as needed (typically 3.5 wci on residential applications NG). Look at your pilot flame: the TC should bifurcate the flame across the top ~3/8", blue, stable flame, TC not completely cooked red (hint of red usually ok but refer to mv PMI). Note that many mfrs will flatten the TC near the cold junction and stamp markings. This is not a defect/ damage. Twisting or breaking the outer copper jacket is. See mv readings. BTW, if the open circuit mv on just a TC peg at 30mv or even higher on LPG, consider lowering the pilot flame . On thermopile systems, we set the open circuit mv around 500mv so it does not cool the tip off (LPG notorious for cooking tips off TC's) . Pilot burner flames too hot can overheat the entire TC, thus losing the 400F differential btw the hot and cold junctions for the Seebeck Effect to work. Check the pilot orifice- did someone ream it out or is it a NG running on LPG? Also, an incorrect pilot assy. can cause nuisance dropout. BTW, the Flame Failure Response Time for a 30 mv TC per ANSI is 180 seconds. You should be conducting a dropout test on every ignition system. Electronic ignition systems vary per mfr. so look up for that system. Can range from 0.5-7 seconds typically before it attempts re-ignition.

If the pilot flame is stable at standby but flutters at call for heat, measure the draft pressure in the stack and overfire. High draft can cause the pilot flame to pull-off .

You should also be running combustion analysis .

HTH,