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I clocked the meter based on instructions I found here and it would appear the boiler is under firing, by a lot.

Rating plate is 262,500 BTU, and I’m getting 124,500. (Formula is 30 seconds for one cubic foot, so 3600/30 x 1035BTU).

Not sure what the flame should look like, but can see a fair amount of orange, and flickering, which seems not good?

is there a way to determine whether the problem is related to gas pressure vs. the boiler?

Yes. Thanks for the heads up. I've merged the duplicate discussions into one here. Thanks!

Honeywell use to make several L91 pressure controls. Some just had a modulating setting. Some had the modulating setting and a "differential. The #s used to be L91A with no differential and L91B with differential if I recall correctly.

I seriously doubt it's the motor. I would say widen the differential if you have an adjustable control. If no you may have to change the control.

Also, when the L91 modulates and constantly hunts it will tend to burn a spot on the potentiometer in the L91.

To test it you could buy and adjustable potentiometer and wire it in place of the pressure control and see how the motor responds.

#30112A @ Supply House.com. But the price is outrageous.

If you disconnect the pressure control and use a jumper to drive the motor up and down (R-B then R-W) the motor should be good. It is usually the control.

Several thoughts.

Why would you need vinegar for vents? There shouldn't be any mineral buildup because they should only be seeing pure steam / distilled water.

All of my Gortons are now going on 13 years old. No issues that I'm aware of.

I haven't touched or cleaned any of them. But, they rarely get hot and steam is practically never at most of them. A few nights ago I heard the vents on the Macon TRV's clicking and I heard a few Gorton's sniffling, so they were hot but that was at -5F.

My Gorton 1 main vents obviously always see steam and those are actually older. Most are from 2011.