COLD STEAM HEAT RADIATORS - CONTENTS: How to Troubleshoot & Fix Cold Steam Radiators in 5 Steps - a complete diagnosis & repair guide & checklist for cold steam radiators. Diagnose & fix radiators that are too cold or too hot.
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How to diagnose & fix a too-cold steam radiator?
No steam system heat in some or all building areas? What to check first. Troubleshooting cold steam radiators: this article describes the diagnosis & repair of cold steam heating convectors or steam radiators.
We also describe how to fix a steam radiator that is too hot and we include warnings about other radiator or baseboard types that are too hot or that overheat.
And we list less common causes of cold steam radiators in buildings and we describe how to fix these conditions.
Cold Steam Radiator Diagnosis Step 1: Check the thermostat & the steam boiler
Make sure that your room thermostat is set to a temperature higher than the temperature in the room - so that it is calling for heat.
Make sure that your heating boiler is working, that is that the heating boiler turns on and off normally. A steam boiler will usually turn on right away in response to the thermostat being turned up or on a call for heat.
Step 2: Check the radiator control valve
Make sure that the control valve at the heating radiator is "open" or "on" as we describe just below.
It's standard to ask first "is the radiator valve turned on or "open" (fully counter-clockwise)?
Experts warn that a radiator slow to heat could have a supply valve that is too small (the problem would always have been observed since date of installation) or a supply valve that is partly closed (the problem would have originated when the valve was closed and would go away when the valve is fully opened, provided the valve is undamaged and really opens internally when its handle is turned.)
We also see both radiators and other forms of steam or hot water heat that are not hot enough if the supply piping is undersized, a valve is partly closed, piping is clogged or blocked, or the hot water flow rate or for steam heat the rise of steam is too slow.
Other problems can cause a steam heat radiator to stay cold when you want heat as we explain next where after the above digression we continue our diagnostic and repair advice for cold radiators or convectors in steam heating systems.
Step 3: check the steam vent on the radiator
If some of your steam heat radiators are not getting hot, the steam vent may not be working, may not be venting at all (radiator stays cold) or may be venting too slowly (radiator heats to proper temperature but too slowly)
If a steam radiator valve is open but the radiator is still cold, the steam vent may not be working.
Our photo at left shows a typical steam radiator vent.
When steam is first rising in the heating system, the steam heating radiator will be cool as will be the steam vent. The vent opens, allowing rising steam to enter the radiator by pushing air out through the vent.
When the steam radiator and steam vent are warm or hot, the vent closes. If a steam vent stops working, rising steam cannot enter the radiator and it will be slow to heat or may not heat at all.
also STEAM HEATING SYSTEMS for details about the choice, installation, diagnosis & repair of steam radiator vents - a common source of cold steam radiators, slow to heat steam radiators, even overheating steam radiators and that incessant hissssssss or spitting condensate when a steam vent doesn't close as it should.
Step 4: Check which radiators are not getting hot - check radiator slope
Steam radiator sloped the wrong way - steam condensate blockage
As our Carson Dunlop sketch shows (above, left), steam radiators can be sensitive to exactly how they are installed and pitched or sloped.
You'll want to learn if your steam heating system is a "one pipe" or a "two pipe" design, but in either case, if the steam supply or condensate return piping have been moved or settled so as to have lost the proper slope, correcting those conditions may be needed.
That's because condensate, produced by cooling steam in the radiator, has to be able to drain back out of the radiator.
A steam radiator that is sloped the wrong way, perhaps due to building floor settlement or a change made by an inexperienced re modeler, will become partly or even completely blocked by accumulated condensate, leading to loss of heat.
Steam heating system controls, inspection, diagnosis, and repair are discussed beginning at STEAM HEATING SYSTEMS.
Step 5: Check these other causes of cold steam radiators
Internal leaks in the steam boiler can cause cold radiators - diagnosis:
Small boiler leaks can be hidden from view: As reader Robert discovered and kindly explained in our FAQs section below, several clues can point to an internal leak in the steam boiler.
A relatively small leak in the steam boiler may never show up as water on the floor around the boiler - the leaking water may just evaporate on boiler internal surfaces. A larger steam boiler leak will probably show up as water on the floor, boiler running continuously, or if the leak is fast enough, a low-water cutoff switch will shut down the boiler.
Watch out: as Robert points out below, leaks in the condensate return system increase the rate of water feeding into the steam boiler. Abnormally high water feed rates into the boiler can in turn speed up corrosion within the boiler leading to costly or even ruinous leaks in the steam boiler itself.
The rate of corrosion will vary depending on not just the water feed rate but also other factors such as the water chemistry and the overall boiler on-time.
Check boiler steam pressure - lower than normal steam pressure can result in heat being delivered too slowly to all radiators, slower heat or even no delivery of heat to radiators on upper floors. If all of the lower floor radiators in a building heat up but none of the upper floor radiators do so, or if no radiators near the end of the steam risers get hot, low steam pressure could be the problem.
Don't rush to "fix" this by changing the steam pressure control switch - that's treating the symptom not the illness.
Check the steam boiler water usage rate - an increase in water usage at the boiler can be due to a leak somewhere - in the condensate line, or in the case of cold radiators, in the boiler itself.
Steam boiler operating problems that can lead to inadequate heat - radiators not hot enough or distant radiators not heating up - diagnostic checks.
Steam boiler problems: An oil or gas fired steam boiler may fail to deliver enough heat for a number of reasons pointed out by ITT , including:
Poor fuel quality
Improper attention or firing (lack of maintenance, burner not firing properly)
Boiler is undersized - if this is the case the heat inadequacy would always have been present but may not be noticed until very cold windy weather
Improper steam piping - as above, if this is the case the heat inadequacy would always have been present or present ever since steam piping has been changed or modified.
Improper arrangement of boiler sections
Lack of boiler cleaning/maintenance, leaving soot in the boiler. Soot acts as an insulator, slowing heat transfer from the fire into the boiler water
Improper firing rate of oil (nozzle size, fuel unit pressure) or gas
Steam pipe problems: The steam pipe feeding the radiator is under-sized or is not properly sloped (steam supply pipes in a one pipe system also return the condensate and must slope away from the radiator and down towards the boiler - always) - (the problem will have always been present but may not be noticed until very cold weather)
Air vent problems: The drainage tongue on the air vent has become damaged or lost or corroded away
Two pipe steam system radiators fail to heat - check these
Radiator pitch problems: doesn't slope towards the steam trap - the radiator should slope away from the steam supply valve and towards the steam trap
The radiator steam trap is clogged, damaged, or stuck closed
The steam pipe feeding the radiator is undersized or the condensate return not pitched properly, leading to blockage
Steam convectors or "unit heaters" are not putting out enough heat
Dirty heater coils - check for dust or debris blocking the fins on the heater coil - see our photo at left
Dead unit heater fan - if the unit heater such as a ceiling-mounted garage heater is driven by a blower fan (not just a convector (driven by gravity), check that the fan operates normally
Blocked steam piping feeding the unit or within the heating coil - due to air or water blockage in the piping
Also check these more technical problems with unit heater heat output:
Design mistakes: the unit is too small for the heated space (the problem will not be new), or the unit has been improperly located - too far from exterior walls can leave cold areas between the heater and the exterior wall;
Improper installation: the steam pipe supplying the unit may be inadequately insulated, improperly sloped, or routed through a cold area where it loses too much heat
Abnormal or too-low steam pressure in the system (there may be hidden leaks in the system)
Maintenance problems: oil and debris in the steam, coating the heat transfer surfaces of the interior surfaces of the heating coil itself
Steam system design or building heat loss rate problems If the steam radiators get hot but the building does not get warm enough, check these
The number of radiators is inadequate, or some radiators are turned off or not heating for other reasons - the remaining radiators can't keep up with the building heat loss rate. You'll notice this more in colder windier weather
The building is losing heat too rapidly for the heating system to keep up. If this is a new problem look for a new draft - a window left open, an attic door or pull down stair left open, etc.
The steam pressure is set too low - steam doesn't rise to upper floors or rises too slowly. Check with your service technician as other problems such as a boiler leak or condensate return leak can result in low steam pressure.
Building design, such as many open stairwells, high ceilings, can make it hard to heat - this problem will have always been present.
If your steam radiator is too hot in a two-pipe steam system, according to the U.S. DOE, check the steam traps:
In two-pipe systems, older steam traps often stick in either the open or closed position, throwing off the balance in the system. If you seem to have problems with some radiators providing too much heat and others providing too little, this might be the cause.
The best approach is often to simply replace all the steam traps in the system.
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 The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
 Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
 The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
 Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones