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Steam pressure gauge and pressure control switch on a WeilMcLain Model 68 steam boiler (C) Daniel FriedmanSteam Boiler Pressure

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Steam heating boiler pressures:

This article describes the normal operating pressure range for residential steam heating systems and for commercial or high-rise building steam heating systems. We include citations of steam boiler explosions and describe probable differences in boiler explosion causes between early steam heat history and modern steam boiler use. The article also provides links to details about the pressure control and safety controls on steam heating systems & boilers.

This article series provides an illustrated inspection and repair guide to Steam Heating Systems. The page top photo shows a modern steam heating boiler.



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Steam Heating Boilers Operating Pressure Settings

Steam boiler pressure control switchResidential steam heating systems are almost always designed to operate at very low pressures, typically around 0.2 psi to a maximum of 0.5 psi - that' s 1/2 of one psi. Click to enlarge and you can see the actual pressure settings on the steam boiler control shown at left.

Watch out: If your residential steam boiler is operating at higher pressures that may be an indication that a service technician or owner was having trouble getting heat distributed through the building. Rather than finding and fixing the problem, someone is trying to "force" the steam around the system.

[Click to enlarge any image]

High rise buildings and larger facilities using steam for heating may employ a high-pressure steam heating system. According to a University of Idaho engineering text we cite below, a 30 psi high pressure steam system might provide sufficient pressure to deliver steam heat to a building 40 stories in height. So we might see 15 psi for a 20 story building steam system.

Why Might Steam Pressure Be Set Too High?

An experienced steam heat service technician will look at the operating pressure of your steam heating boiler and if it is not set to a normal level, the technician will look for the reason. Examples of problems that can affect the flow of steam heat through the system, leading to attempts to over pressurized the system include

For details about radiator problems see RADIATORS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Watch out: do not modify a steam boiler pressure control switch to try to force steam heat to cold radiators or to higher floors. Doing so makes the system less efficient, fails to find and correct the underlying problem, and in some situations it could make the heating system unsafe.

Steam Boiler Pressure Control Safety Switch Operation

Steam pressure control switch

The pressure control switch on a steam heating boiler is designed to shut the heating system down should unsafe high pressures develop.

As we emphasize at our description of pressure gauges on a steam boiler, residential steam heating systems are almost always designed to operate at very low pressures, perhaps around .5 psi - that' s 1/2 of one psi. You should see similar settings on the pressure gauge and on the steam pressure control switch (the gray box our photos of steam pressure switches shown here) on your boiler.

Because the operating temperature, pressure, and form of heat distribution are different from hot water heat (typically 20-30 psi of hot water), steam boilers (typically less than 0.5 psi steam) use use controls that monitor steam pressure operated controls like the Honeywell steam pressure control shown below.

Steam boiler pressure control switch

Reader Question: the gray box on my steam boiler is set under 2 psi but the boiler pressure is 7-8 psi. Is this normal and safe?

Steam boiler pressure control switch (C) Daniel FriedmanThe gray box on my steam boiler is set low (less than 2psi) but the glass pressure gauge is reading 7 or8 at times. Is this normal /safe? - Brian 11/21/12

Reply:

Brian,

One wouldn't expect a boiler to blow up at 14 psi, but I agree that the system is not set nor operating at safe normal pressures. I suggest calling a service tech promptly.

Usually residential systems operate at lower pressures, less than 1 psi, often around 0.2 to 0.4 psi.

Since your steam boiler pressure control valve is set under 2 psi and the boiler pressure is way over that, and assuming that your steam boiler gauge is working and not "stuck" at an abnormal reading , the problem may be the pressure control valve itself.

See STEAM PRESSURE GAUGE
or
See PRESSURE SWITCH, STEAM BOILER.

We discuss how to set heating system pressures for both hydronic boilers and steam boilers over
at PRESSURE & TEMPERATURE SETTINGS, CONTROLS

Also see RELIEF VALVE, TP VALVE, STEAM BOILER.

Reader follow-up: changing out the steam pressure control valve did the trick

got the tech. he took off the gray box on my newly installed williamson boiler (2 weeks ago) and replaced it with the one from my older rotted out 12 year old Burnham! both gray boxes are honeywell and seem to be identical. works ok now. go figure!

Steam Boiler Pressure Gauge and Normal Pressure Ranges

Steam pressure gauge on a steam boilerPressure and Temperature gauge on steam heating boilers: Residential steam heating systems are almost always designed to operate at very low pressures, perhaps around .5 psi - that' s 1/2 of one psi.

You should see similar settings on the pressure gauge (at left in our photograph) and on the steam pressure control switch (the gray box at right in our photo) on your boiler.

Details about gauges on steam heating equipment can be read
at GAUGES ON STEAM BOILERS

If your heating system uses forced or gravity circulated hot water rather than steam, controls and gauges are different:
see GAUGES on HOT WATER BOILERS

or see PRESSURE GAUGE, BOILER for more details about pressure gauges on hydronic (hot water) heating boilers. These are not steam systems.

Reader Question: proper setting for a Honeywell PA-404-A 1099 Presstrol on a steam boiler

Does anyone know the proper setting for a honeywell pa-404-a 1009 prestrol control for a weil-mclane steam boiler - Rick 9/11/11

Reply:

Rick the exact pressure needed varies by installation but in a low pressure residential steam system the pressure range is usually between 0.2 and 0.4 psi.

Reader Comment: too-high steam pressure traced to a blocked sensor on steam pressure control

Pressure on gas steam boiler was rising far too high, so high that the pressure relief valve released twice when it hit 15 psi (as it was supposed to do). Good buddy who really knows his stuff checked everything from pressure valve to pressuretrol. Nothing . He then checked "pigtail" and found blockage .Problem solved!! - Ken 11/24/12

Reply:

Thanks for this note it may help other readers

Reader Question: 28 psi and water coming out of my return on my American Standard boiler

II have a pressure of 28 psi and water is coming out of my return how can i lower the water pressure from my steam American standard boiler - Ronald 1/13/2013

Reply: 28 psi on residential steam heat is very unusual, probably unsafe - shut the system off

Ronald,

Watch out: If your heater is a residential steam heating system it is operating at an abnormally high temperature and is unsafe. Turn the system off immediately and call your heating service company.

If your heater were a residential hot water heating boiler (hydronic heat) its pressure might be close to the upper end of normal operating pressure - and the leak at the valve could be due to a valve problem or to any of quite a few other causes. See RELIEF VALVE LEAKS for procedures to diagnose and fix leaky TP relief valves. See the links just below for information on how the steam heating system pressure is controlled and set.

Steam Boiler Accidents & Explosions

Steam boiler explosions early in the history of steam boilers were often related to leaks, loss of water in the boiler, absence of safety controls like the HARTFORD LOOP and LOW WATER CUTOFF VALVE. In modern steam boiler explosions we are of the opinion that other forces might be at work, such as improper maintenance, tampering or work performed by inadequately-trained personnel.

References for Steam Heating System Pressures & Temperatures

All of the steam heating system controls described in our introduction are illustrated below and described in greater detail in individual articles found in this steam heat series.

...


Continue reading at COLD STEAM HEAT RADIATORS - diagnose & repair, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see PRESSURE & TEMPERATURE SETTING, CONTROL FAQs

Or see RELIEF VALVE, TP VALVE, STEAM BOILER

Or see STEAM BOILER TEMPERATURE

Or see STEAM HEATING SYSTEMS & CONTROLS - home

Or see WATER FEEDER VALVE, STEAM

Suggested citation for this web page

STEAM BOILER PRESSURE at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

INDEX to RELATED ARTICLES: ARTICLE INDEX to ARTICLE INDEX to STEAM BOILERS

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