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AFUE DEFINITION, RATINGS
AGE of HEATERS, BOILERS, FURNACES
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER VALVE, HEATING SYS
BANGING HEATING PIPES RADIATORS
BOILER CONTROLS & SWITCHES
BOILER LEAKS CORROSION STAINS
BOILER NOISE SMOKE ODORS
BOILER OPERATING PROBLEMS
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
CHEMICAL TREATMENTS for BOILERS
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CIRCULATOR PUMPS & RELAYS
DEFINITION of Heating & Cooling Terms
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATORS, DAMPERS, BOOSTERS
FILTERS, OIL on HEATING EQUIPMENT
FIRE SAFETY CONTROLS
FLOODED HEATING EQUIPMENT REPAIR
FLUE VENT CONNECTORS
FREEZE-PROOF A BUILDING
FUEL OIL TYPES & CHARACTERISTICS
FUEL UNIT, HEATING OIL PUMPS
GAS BURNER Flame & Noise Defects
GAS PIPING, VALVES, CONTROLS
GAUGES ON HEATING EQUIPMENT
HEATING COST SAVINGS METHODS
HEATING LOSS DIAGNOSIS-BOILERS
HEATING OIL PIPING TROUBLES
HEATING SYSTEM INSPECTION GUIDE
HEATING SYSTEM NOISES
HIGH EFFICIENCY BOILERS/FURNACES
LP & Natural Gas Safety Hazards
MANUALS & PARTS GUIDES - HVAC
MOTOR OVERLOAD RESET SWITCH
NO HEAT - BOILER
NOISE, HEATING SYSTEMS
ODORS FROM HEATING SYSTEMS
OIL PUMP FUEL UNIT
PUFFBACKS, OIL BURNER
RELIEF VALVES - STEAM TP VALVES
Reset Switch - Heater Primary Control
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
SAFETY, HEATING INSPECTION
SAFETY RECALLS, Chimneys, Vents, Heaters
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCHES - Flue Gas DetectionS
STACK RELAY SWITCHES
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
VIDEO GUIDES: Heating System Videos
Steam heat controls: here we provide a photo guide to all types of controls found on residential & light commercial steam heating systems. We tell you what each control does, where it is located, what it looks like, and we link to in-depth information about setting controls or diagnosing & repairing problems with steam heat controls. This article series provides an illustrated inspection and repair guide to Steam Heating Systems.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
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.
If you don't know what kind of heat your building uses, we explain how to figure out the answer at HEATING SYSTEM TYPES.
If your heating system is not working properly, see NO HEAT - BOILER.
Sketch of a one-pipe typical steam heating system (left) is provided courtesy of Carson Dunlop Associates.
In a one pipe system each radiator is served by a single pipe: steam rises into the radiator and condensate (water) returns from the radiator through the same pipe loop, as you can see at left.
A two-pipe steam heating system is similar but provides a separate loop of piping that collects condensate and returns it from the radiator to the boiler.
List & Photographs of All Controls found on Steam Heating Systems
If your heating system looks like a heating boiler but your heating radiators have valves which hiss and let air escape as heat is coming on your heat is probably being delivered in pipes which circulate steam from the steam boiler up through radiators in the occupied space.
Although both hot water - hydronic heating systems (discussed at BOILERS, HEATING) and steam boilers (discussed here at STEAM HEATING SYSTEMS) use a boiler that heats water, the heat distribution method and most of the heating boiler controls are different between these two systems.
Both steam boilers and hot water boilers may share certain controls that monitor and manage the heating source such as an oil burner or gas burner. Heater burner controls make sure that there is a safe proper combustion flame, control draft, and protect against flue gas spillage. Examples include the CAD CELL RELAY SWITCH (oil burners) or Spill Switches (gas burners).
Steam Boiler pressure controls:
Invented by the Hartford (CT) insurance company in response to an unacceptable rate of steam boiler damage, loss, and even explosions, the Hartford Loop is a piping arrangement at the steam boiler condensate return line that allows condensate to re-enter the boiler but prevents complete loss of steam boiler water should a leak develop elsewhere in the condensate return line.
The risk of steam condensate return water leaks was and can remain significant because of the corrosive acids that form in steam and other heating boilers and because not coincidentally, the more likely place where such leaks would develop is in the last and lowest run of the condensate return line along or close to the floor approaching the steam boiler.
Above are photographs of a couple of different but still modern automatic water feeder valves on a steam boiler.
Low pressure steam boilers still require a pressure/temperature safety relief valve. A pressure relief valve is a spring-loaded device that will open to spill excess pressure (and temperature) in the form of water, steam, or a mix of the two, at a pre-determined pressure in order to protect the heating appliance from damage, or worse, a dangerous BLEVE explosion. (BLEVE EXPLOSIONS)
However the valve operates at different temperatures and pressures than found on a hydronic (hot water heating) boiler. Residential steam boilers typically operate at below 1 psi, and on residential steam systems the pressure/relief valve is usually set to open at 15 psi.
If your boiler pressure/relief valve is leaking see RELIEF VALVE LEAK for the steps in problem diagnosis & repair.
Our steam boiler TP relief valve photo at above left shows typical operating parameters for these safety controls. This particular valve, a Watts No. 315-M1 is a 3/4-inch diameter valve set to open at 15 PSIG and has an energy release rate of 375 LBS/Hr.
The steam heating boiler TP valve shown at above right is leaking and lacks its discharge tube - this is an unsafe installation.
Steam boiler TP relief valve photo contributions needed - . CONTACT us.
Our photo at above left illustrates a steam condensate return pump system in a home
Our second steam condensate return system (above right) shows the reservoir and condensate pump motor (gray pump and new piping on the right side of the condensate reservoir at the left in that picture). This system also includes chemical injection into the steam condensate.
Details about steam condensate piping, return pumps, and leaks are found at CONDENSATE RETURN PIPES, PUMPS, STEAM
Frequently Asked Questions (FAQs) about Steam Heating Boiler Controls: installation, diagnosis, repair
Question: is replacing the steam boiler sight glass difficult?
Is replacing the sight glass on a Weil McClain steam boiler difficult? - Carl 4/17/11
It's not mechanically difficult to replace the steam boiler sight glass, but you have to shut down power to the boiler, let it cool down, and drain down the water level in the boiler low enough to be able to disassemble the fittings and install the new glass.
I should add that on some steam boiler sight glass setups the shutoff valves are working and you might be able to just shut off water there provided the boiler's not too hot to work on. The ease of slipping in the new sight glass depends on its fittings and their condition.
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
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.
Question: steam pipe configuration question at the boiler
what's the term they call the 2 steam pipes that form an H above a steam boiler. in other words the pipes from both sides of the burner connected together?THANKS,Walter - 9/25/11
Reply: steam pipe header
Walter: sorry we couldn't give an instant reply; sometimes the volume of reader questions is considerable and takes some time to get thorough.
Question: steam boiler parts identification
Wow, what a great web site. I am trying to identify a vessel on the side of an old National steam boiler/furnace. It is about 12-18" tall, about 8" diameter and is attached to a manifold in the side that is about 12" off the floor. It is heavily rusted. The boiler is an old coal fired converted to oil. Can I send you photos? Thanks, Stephen email@example.com or strentsch 10/4/11
sure Mr. Strentsch,
Question: where do I add water to my furnace
Need to know where I add water to my furnace. The low water indicator is on. Not sure where to look. And not sure if I have an automatic water feeder. Thank you LJV 109/23/11
Question: My steam boiler seems to be taking more water than usual
I blow the system down regularly and then make up the water in the sight glass. However I seem to be using significantly more water then years past whereas I'd top the sight glass every couple of weeks in the past compared to every other day now. What do you think the problem is? - Tom C 10.27.11
Tom C: a common reason for increased water consumption in a steam heating system is one or more radiator steam vents that are not closing properly. Check also for a leak in the condensate return line.
Question: I need to prepare for a steam boiler license and want book recommendations
I’m happy to have found this website. I’m getting back into heating and cooling and need to prepare for higher license. Question: Is there a DVD collection you recommended as an additional studying tool? I see that Harold J. Frost, Frederick M. Steingress, Daryl R. Walker’s collection is close to 600.00 which is very steep for my pocket. Would you happen to know of a website or cheap place I can buy such DVD or a CD? If not these guys than another author is ok. Thanks for the feedback. Kym 11/23/11
Kym if you are looking specifically for information on steam heating I'd pick up any of Dan Holihan's books on steam heat. He's the best.
The HomeServ tech just left after installing a new auto water feeder, and the PSI gauge on my steam heater is off the chart, over 30 PSI. I shut it down and called HomeServ and they said leave it on and they'll come in the morning. How do I lower the PSI myself so I can leave it on tonight and my little kids (two with strep) don't freeze? Thanks! 2/22/2012
Watch out: If the PSI gauge is showing abnormal pressure and the gauge itself is working properly the system is unsafe and should be shut down. Call someone else and fire that tech - from your description the system sounds unsafe
Question: water drips out of the air valve at the bottom of the tank
I HAVE AN OIL BURNER HOT WATER SYSTEM MY EXPANSION IS DRIPPING WATER OUT THE AIR VALVE STEM AT THE BOTTOM OF THE TANK SHOULD I REPAIR OR REPLACE - Mike S 10/12/12
Mike, the air valve stem is replaceable, I would tr that first. Check also for abnormal system press ( an unsafe condition)
Question: what are those red knobs above and below the sight glass on my steam boiler and which way do I turn them
What are the red knobs above and below the sight glass for and how should they be turned? - Anon 10/15/12
The red control valves at the top and bottom of the steam boiler sight glass are water shutoff controls used to isolate the sight glass from the boiler to permit glass replacement should it break. Closing both valves also permits emergency, temporary heating system use if the glass is broken, though of course you no longer know the boiler water level.
Question: radiator banging noise repair procedure
I have a one pipe steam system. My dining room radiator air vent was just replaced because the old one was leaking profusely (damaged my floors). The porch radiator air vent was also replaced because of too much steam condensation in the room, but now the open/close valve is leaking at the base. The radiator upstairs in middle bedroom is banging and clanking. The pipe that runs along the basement ceiling (finished basement) also bangs when the heat is coming on. My plumber cannot really give me an answer. Any suggestions would be appreciated. Thanks p Rita 11/21/12
Question: relief valve is leaking
cleaned on a vav system is leaking dose the cilanod valve need to be replaced- Anon 11/23/12
See RELIEF VALVE LEAKS for procedures to diagnose and fix leaky TP relief valves.
Question: 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
Thanks for this note it may help other readers
Question: trouble controlling level of steam heat - can I close off the radiator
My building uses steam heaters. I have no control over the heat in my unit because the thermostat is controlled by my landlord/owner who lives above me. However I have a small 1 bedroom with two heating units so even with all of the windows open, it can still get very hot. Is it okay for me to completely close the "open/close" black knob valves on my units or will that cause problems for the whole system? My landlord had previously told me not to touch the valves... Emily 12/10/12
Yes if the radiator control knob is not jammed or frozen you can try closing it partly or fully; radiator control knobs are intended to be a homeowner-resident-operator control. But if the knob is not easy to turn, don't force it as you might end up with a leak.
Question: hissing boiler
I have 2 yr. Boiler. It hisses like venting steam off and on loudly. Seems like when heat comes on venting starts until off. -Mr. Ed 12/28/12
Steam boilers include steam valves that hiss; we need more details.
Question: leaky relief valve
I am having a pressure problem and it looks like one of my relief valve is leaking or letting the pressure out would this keep my boiler from running. It seems to be shutting off and I need to set the pressure all the time. is it as simple as changing the valve and resetting the Pressure? Rick 1/3/2013
See RELIEF VALVE LEAKS for procedures to diagnose and fix leaky TP relief valves.
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
Watch out: If your heater is a residential steam heating system it is operating at an abnormally high temperture 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.
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?
We discuss how to set heating system pressures for both hydronic boilers and steam boilers over at PRESSURE & TEMPERATURE SETTINGS, CONTROLS
Also see RELIEF VALVES - STEAM TP VALVES.
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!
Questions & answers or comments about residential steam heating system controls, valves, gauges
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