Gauge glass / feeder level vs. boiler water line

Precaud

This question is prompted by another current thread in this forum.

My boiler has an M&M #47-2 combined LWCO and auto-feeder. The specs for the 47-2 says it "keeps water level at 3 inches above the center of the lower gauge glass tapping", and also calls this the "feeder closing level", i.e. the level at which the water feeder turns off.

(The newer version says 3-7/16" but the manual for my older one says 3").

On my boiler, that point is 20.75" above the floor (the black mark on the gauge glass).
The actual quiescent water level of the boiler when cold is a tad higher, at 21.25" .

So it appears the feeder is working as it is supposed to.

But the boiler water line is 24" above ground.

So it appears the boiler is always operating with a water level that is at least 3" below its designated operating level. That seems like a pretty large difference.

Is this true?
Is it desirable?
What are the operational consequences of this?
Would I be better off bypassing the auto-feeder and manually restoring water to the proper level as/when needed?

Thanks for helping me understand this.

Jamie Hall

The manufacturer specifies a water line -- but provides a gauge glass. As a general rule, so long as the water line is somewhere in the middle third of the gauge glass, no problem. Lower? you'd really want it higher... raise it manually. Higher? So long as it isn't too much higher, and you have good to excellent near boiler piping, and so long as it is really within the gauge glass, again, should be OK, but there is a risk of additional water carryover.

In my opinion, anyway...

EBEBRATT-Ed

@precaud
This is a perfect example of why water feeders can be bad. People rely on them instead of checking the water level.

Feeders are set to maintain a level above the lowest water level to a safe minimum water level. They do not bring the water level to 1/2 of the gauge glass or the manufacturers water level where they should be.

The MM 47-2 mounts on the gauge glass tappings and the height is not adjustable

Precaud

EBEBRATT-Ed said:

@precaud
This is a perfect example of why water feeders can be bad. People rely on them instead of checking the water level.

Well that's definitely the case here. I have never manually added water except after partially draining it for service. And then, only to the level specified in the 47-2 manual.

EBEBRATT-Ed said:

Feeders are set to maintain a level above the lowest water level to a safe minimum water level. They do not bring the water level to 1/2 of the gauge glass or the manufacturers water level where they should be.

The MM 47-2 mounts on the gauge glass tappings and the height is not adjustable

Thanks for clarifying. To your latter point, yes, I see that. And only now realize the implications. So I take it you suggest I use the water bypass valve to set the proper water level, and only rely on the 47-2 feeder as a failsafe?

EBEBRATT-Ed

@Precaud
exactly right.

Even though you have your car taken in for service doesn't mean you shouldn't pop the hood occasionally to check the oil, trans fluid, radiator etc.

Precaud

OK great. This will also give me a chance to see what the system's water use is like. Indications thus is far is, it's pretty tight. But now we'll see. I'll report back in a week or two.