2 pipe steam system lacking venting

Jamie Hall

Oops. @EBEBRATT-Ed is right (as usual) on the three controls. The pressure settings for them, then, are a little different than what I had said earlier, and the modulating control is the one which needs to allow the steam pressure in the 1 to 2 psi range.

Wvega123

Here is a closeup of the three pressure controls. To the question of how the boiler is activated for DHW in the summer i attach i picture of the aquastat 

Jamie Hall

Oh good. You do have one manual reset. Excellent!

JUGHNE

If the system does run up to 5 PSI, one of those 2 smaller controls should have shut the boiler off before that point.

Either they are truly jumped out in a junction box/burner control box or the pigtails under them are plugged and they do not sense the true pressure.
The newer looking pressure gauge is on a copper pigtail while the controls are on older steel pigtails which plug up easier.

Also the 1" pipe they are mounted on has "crosses" with plugs for clean outs, they should be inspected in their entirety all the way into the boiler.

EBEBRATT-Ed

So the control on the left is a manual reset high limit.

It is a mystery to me what is modulating the burner mod motor. There should be another pressure control somewhere.

On the burner panel there is a round knob that is a potentiometer for controlling the flame size when servicing the burner. There should be a switch near the potentiometer marked "manual-auto". Is that switch in the "manual or auto position"?

The aquastat on the side of the boiler probably operates the boiler for domestic hot water

Charlie from wmass

@EBEBRATT-Ed there are two regular pressuretrols I would guess that one of them would be used for high low fire. Not for modulation.

Wvega123

The switch on the burner panel is set to auto. The manual reset high limit works but i don't know about the other two.

EBEBRATT-Ed

@Charlie from wmass

It is possible they did that but not right. The right control is a Honeywell L91A or L91B which has 3 wires R W and B. Maybe there is another control hidden somewhere out of site or up on the supply piping. If they used one of the Pa404a controls the burner will not modulate. Lo-high fire is all you will get.

Come to think of it some Heat Timer controls have a series 90 output that can modulate the burner maybe that is the answer.

Charlie from wmass

@EBEBRATT-Ed on large residential like apartment buildings I have only seen low high low fire controlled by a simple pressure switch. Not many tube boilers where I work so that may be why. 

CLamb

Before jumping to the conclusion that the Pressuretrols are not working I would check to see if that pressure gauge is working correctly. Does it drop to zero when the boiler is cool? Ideally, there should be a lower range pressure gauge, like zero to three psi as well.