Setting steam boiler pressure cutoff

[JKevorkian]

Last winter my gas-fired boiler refused to fire, even after replacing the low-water cutoff switch, the pilot generator, and eventually the gas valve. After poking and prodding everything that seemed to move, I lifted the indicator on the steam pressure cutoff box and the burners finally lit off. When I took my fingers off the indicator, the burners went out. "Hmmm", thought I. "Another adjustment that probably went awry." I turned the screw at the top of the switch box until the burners lit and stayed lit and congratulated myself on my brilliant deduction. I awoke the next morning to a great whooshing noise emanating from the basement, and discovered the room full of steam. The relief valve on the boiler was open and gushing steam "everwhar". Ot was so damp down there, the flourescent lights wouldn't go on. After filling the boiler with cold water to bring the pressure down, and exhaustiing the steam outdoors with a fan, I turned the cutoff switch screw back to where I thought it was originally. Of course, the boiler wouldn't fire again, and I finally discovered that that curly pipe going to the bottom of the switch box was plugged with rust. I replaced the pipe, and the furnace has been working dependably since then. However, one thing concerns me: The pressure gauge on the boiler reads around 4-7 lbs when it's really humming since we've had this cold spell, and I think the cutoff switch isn't adjusted correctly. The boiler never exceeded 2 lbs. back in the days before things started wearing out on the unit. Can anyone enlighten me as to the proper adjustment procedure for the steam pressure cutoff?

[Oscar_Lives]

Do you think we are nuts? Do you think we want to be accomplices to murder?

[buffalobill]

you might search for the manuals online thru www,google.com for not just the main boiler but the individual controls. read them. name them with a sharpie marker and name the pipes and arrow them for direction of flow. if you post some nice picture links here at alt.home.repair somebody may recognize the general operation of your system. but you should hire a local boiler old-timer because the balancing and setting of the devices in your system varies with the design for your home's layout. take notes. make signs on the devices, and develop an annual checklist for your system. also dumping cold water into some systems under some conditions can damage your boiler.

[Edwin Pawlowski]

Most boilers operate in the range you have it, or a little lower. Maximum is usually 10 pounds, the safety low off is usually set at 15 pounds pressure. Higher pressure means more heat is being carries to the radiators. If 2 lbs. worked, set it back to that range.

I don't know the specifics of your boiler. Some have a high fire and low fire range. That means the unit starts out on high fire, reaches a set pressure, then goes down to low fire and stays there until a drop send it back to the high fire position. You may or may not have that.

One caution here. The overpressure you had may have been a PITA, but did not do any damage to the boiler. However, letting in a lot of cold water can cause problems, such as cracking cast iron from stress. Then you'd have a very expensive mess on your hands. Never put cold water into a hot boiler.

[HeatMan]

Some boilers work best at a cut-in of one-half pound and a cut in of one pound..

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[David Efflandt]

Ouch! The PressureTrol on Most steam boilers should be set per another reply with 0.5 psi cut-in and 1 psi rising differential cut-out (or if it does not go down to 0.5 it may be a control that you set to 2 psi cut-out and 1 psi decreasing differential cut-in). In other words it should operate between 0.5 and 1.5 psi (not more than about 2 psi). Systems with a Vaporstat run even lower (in ounces of pressure).

Most steam radiator air vents only work well up to 1.5 to 2 psi. Any pressure higher than that just makes the steam heavier, slower, and less efficient (costs more money).

If your pigtail was plugged, your pressure gauge might be too. When I bought my home, the steam pressure was cranked way up (causing loud hissing of air vents), a snubber on the pressure gauge was blocked, but the gauge itself was stuck (would not go to zero when removed). Since I replaced the gauge and set the pressure as low as it goes, it has worked perfectly.

[Edwin Pawlowski]

Depends on the system. I have a low pressure setup that runs between 5# and 9# with a cutout at 11#. I also operate two boilers at 110# with cutout at 120#. They modulate depending on load. We use about 8 to 10,000 gallons of water a day to make steam.