Intermittent LGB-11

grrrdot

I’ve got an LGB-11 with an intermittent issue. When its acting up it lights off all the burners but fails to high fire, then just retries forever.

Acts like the high fire control module is not seeing flame, we replaced its flame sensor which worked for a week but now its acting up again but always ends up working again while testing.

Check out the photo. The high fire module on the right has the flame sensor ground running to the chassis, ( just visible in the bottom left corner of the photo )
Then the spark lead ( spark isn’t needed ) grounds to the chassis through the foot of the pilot module…

Is this right? Minimally shouldn’t Ground run to the burner assembly?

HVACNUT

This shows where all the grounds go. Any gas pressure readings? Pilot tube, assembly, orifice all good? Pilot adjustment?

The Steam Whisperer

I had a similar problem in the past. Tiny spiders had built a web in the gas orifice for the far right burner tube where the flame sensor is located. It's so far over to the edge, you won't notice it not burning properly. We've also had a defective gas valve on a new LGB rather recently, IIRC. The valve was not properly adjusted to the correct gas pressure from the factory causing the flames to lift off the burner and not allowing the current to move through the flame for the sensor. Its hard to get a manifold pressure reacing when you can't get the boiler to remain on high fire. We ran it on low fire only until we were able to finally figure out the issue. If the gas valve says Honeywell on it, the possibility of a defect is very high.

AS an FYI, out of the 15 years I've been back in Chicago, we only have a couple of LGB's running on full fire, one we sized and installed and another couple besides that. All of them are so oversized, that we run low fire only. The systems work much better, especially with the incorrect header piping on nearly all of the installations. Low fire keeps the water in the boiler much better.

To give you an idea of the boiler size necessary, an LGB-11 is about the midsize boiler needed to heat a 3 story, 50,000 sq ft courtyard building steam system in Chicago. If its hot water, then a much bigger building typically could be heated.