Guide to Finding & Fixing Leaks in Heating Radiators, Baseboards & Convectors
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How to identify, inspect, diagnose, and repair problems with hot water or steam radiators, baseboards, or heating convectors
How to inspect, diagnose, and repair problems with steam radiators
If your radiator or baseboard is cold and the heating system is "on" - here we diagnose the problem
Where leaks occur on hot water and steam radiators, convectors, and baseboards
Guide to unusual radiators, baseboards, and heating convectors in buildings
Questions & answers about diagnosing & fixing leaks in hot water or steam heat radiators

Heating radiator leak troubleshooting: This article describes the types and locations of leaks found on heating radiators: hot water, steam, cast iron, heat convectors, baseboard heat, electric heating convectors.

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Our page top photo shows a common point of leakage on cast iron radiators, between abutting radiator sections near the bottom of the unit.

This website answers most questions about all types of heating systems and gives important inspection, safety, and repair advice. 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 or NO HEAT - FURNACE.

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In addition to cast iron radiators using hot water or steam as a heat source, we describe two other very common hot water heat distribution methods below.

Carson Dunlop's sketch (above left) and our photo of a heating baseboard (above-right) show a typical modern hot water heating baseboard system installation.

Where to Check for Leaks on Baseboards, Radiators, or Heating Convectors

Obviously, first look at the floor around each heating component to see if you see water stains or water damage. (Water damage can occur at steam radiators too, as condensate could be leaking at the condensate return pipe fittings.)

Here are some common leak locations on baseboard heating systems

Heating baseboard leak (C) Daniel Friedman

On heating systems using hot water baseboards, leaks can occur anywhere in the piping system, including at air bleeders located at the ends of baseboard sections, at couplings or elbows in the piping system, or where freezing has cracked or burst a heating baseboard pipe.

Our photo of a leaky heating baseboard (above left) shows that prolonged leaks may rot carpeting (leaving an obvious leak clue once someone vacuums up the ruined carpet at this spot) and may also cause hidden damage to the subfloor or even the structure. Or perhaps a mold problem may result.

Our baseboard piping leak photo (above right) shows how freezing pipes may cause separation at a solder joint instead of actually bursting the piping. In the case shown, the original solder joint had been poorly made, so this was a weak point that broke first.

Leaks at heating baseboard air bleed valves are shown at Air Bleeder Valves. If your heating baseboards are not in fact getting warm when your thermostat is calling for heat and the boiler is indeed running, see AIRBOUND HEAT SYSTEM REPAIR

Also see WINTERIZE A BUILDING for examples of freeze-burst copper forced hot water heating piping in a baseboard heat system.

Here are some other common leak locations on hydronic or steam radiators

Leaks occur between sections of cast iron hot water or steam radiators.

The radiator may leak where sections of cast iron are bolted together, or if the radiator has rusted-through or become cracked, perhaps by freezing, you may see rust and leak stains at splits in the individual radiator sections (photo at left) .

Such damage means the heating radiator should be replaced.

Leaky steam radiator (C) Daniel Friedman

Sometimes a leak at a steam radiator is not critical - you may at least make it through the heating season, or the leaking may occur only when the radiator is cold (photo, above-right, also shown at page top, of a leaky steam radiator). This is a steam condensate leak.

If you see rust stains and leak indications between radiator sections at the top of the radiator, such as in our photo (above-left), or other rust, splits, or evidence of leakage from the body of the radiator, we recommend that you ask for repair advice from your heating service company.

Leaks also occur at radiator valves, at radiator bleed valves, and at the piping fittings where valves and pipes join the radiator bottom or top.

As Carson Dunlop's sketch (left) warns, watch out for hidden structural damage or damaged ceilings below leaky radiator valves.

Frequently Asked Questions (FAQs) about hot water or steam radiator troubleshooting, installation, or repair

Question: repair a pinhole leak in copper baseboard

Im a journeyman plumber and I know how to braze but I'm not sure how to go about repairing a pinhole leak in a copper hot water baseboard heater. Obviously it has to be dry before I can braze it but how do I drain it and once repaired how do I properly fill it up with water and bleed the excess air?

Reply: solder repairs of small leaks in copper heating baseboard piping

The proper repair of a pinhole leak in copper piping would be soldering not brazing. But you'll most likely need to remove the water from the baseboard heater first. Or one can cut out a bad section of tubing or piping and solder in a short section with unions and copper piping of the same diameter. Be sure to properly sand and prep the copper pipe surfaces, remove any burs, and use a soldering paste or flux to assure a good solder connection.

Watch out: often the presence of a single pinhole leak is an indicator of more trouble ahead. Corrosion, or too-thin or defective copper piping may be prone to developing multiple leaks. I'd go ahead and patch or repair the present leak, but I'd keep an eye on the building heating distribution piping and baseboards for more leaks down the road.

Question: are steam radiator leaks dangerous?

I have an old one pipe steam radiator that has a small crack about 8 inches up. It drips a bit but my concern is the steam. Is this dangerous to have expelled into the air as far as breathing quality. I am not sure If it is a health issue. I have some concerns about having It replaced with a cheap one from china. Thanks so much for your help. - Josh (also by email) J.F. Thank you so much for your help.

Reply:

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with leaky radiators, including possible hidden damage from prior or long-standing leaks.

That said, here are some things to consider:

Steam is water vapor, and having been boiled, would not be itself a health concern but

Watch out: steam vapor can cause burns.
A leak of condensate out of your radiator (such as the leak shown at page top of this article) into the building structure risks rot, mold, damage
It might be possible, when the radiator is cold, to repair the crack using a high temperature-resistant epoxy - you'll need to clean the surfaces first. Also,

Watch out for lead paint on old radiators (see LEAD POISONING HAZARDS GUIDE)

Follow-up comment: Harmful chemicals in steam from steam boilers?

Thanks for the quick reply Daniel. I was unsure if chemicals were commonly used in the w

Reply: List of common chemicals found in steam boiler water treatment compounds and reference to their MSDS information

Thanks for the clarification

Indeed some steam heat systems, usually commercial, may contain anti frothing agents and anti corrosive or anti scale agents that remove oxygen from the water and control boiler water pH, or to keep minerals such as calcium and magnesium in suspension (glycerin, Sulfites to remove oxygen, prevent corrosion, alkalinity boosters to reduce the pH and thus control corrosion, phosphates and polymers to keep minerals in suspension and thus reduce scale formation, and amines to "boost condensate" to further reduce corrosion)and it would be reasonable to be worried about some of those chemicals in the boiler water itself. [1] [2] [5]]

Carbonic acid (H₂CO₃) formation in heating boilers and the resultant need for boiler water treatment is discussed at HEATING SYSTEMS

Check with your boiler service company and take a look at the boiler service tag - let me know if any additives were used in your system (unlikely in residential steam boilers) and we can research further by reviewing the MSDS for those products.

Corrosive liquids used in some treatment compounds are skin, lung, and eye irritants (and considered unlikely to be ingested), but you would not expect to find these being released at harmful levels into occupied space from a steam radiator steam leak, since the same steam is also vented quite normally through steam radiator vents during normal system operation.

Phosphate polymer blends are generally considered non-hazardous [3][4]
Sodium Hydroxide (a boiler cleaner) is a corrosive liquid [4]
Boiler water treatments containing Sodium bisulfite, liquid caustic potash, and ethylene diamine tetraacetic acid NA salt or liquid NAOH, or cyclohexamine are also corrosive liquids [4]
Sodium bisulfite (an oxygen scavenger) is an irritant and may be packaged as a steam boiler water treatment along with liquid caustic potash, a corrosive liquid [4]
Aqueous ammonia used in some steam boiler water treatment chemicals is toxic by ingestion and is a lung irritant [4]
Amines used in boiler water treatment chemicals (morpholine or cyclohexamine) in concentrated forms are flammable and are eye and lung irritants [4]
Also see see Boiler Chemicals 101 provided by NCDENR.

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Questions & answers about diagnosing & fixing leaks in hot water or steam heat radiators.

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Additional technical contributors & reference sources for this article are listed below.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

RADIATORS
  BANGING HEATING PIPES RADIATORS
  BASEBOARD, CONVECTOR, RADIATOR TYPES
  COLD HOT WATER BASEBOARD / RADIATOR
  COLD STEAM HEAT RADIATORS
  LEAKS at BASEBOARD, CONVECTOR, RADIATOR
  RADIATOR or CONVECTOR COVERS
  RADIATOR or CONVECTOR INSULATION
  RADIATOR STEAM VENTS
  RADIATOR STEAM VENTS, AUTOMATIC
  RADIATOR VALVES & HEAT CONTROLS
  UNEVEN HEAT DIAGNOSIS

[1] The Chemical Treatment of Boiler Water-Volume 1, James W. McCoy, Chemical Publishing Company, 1981, ISBN 0820603775, ISBN 978-0820603773, and Volume 2, Quoting from the publisher's review:
This is the most comprehensive book for treatment of steam boilers. It is highly technical, and covers every aspect, how, why, when, etc. It is a must read for anyone who maintains boilers for a living. The only downfall is that a background in basic chemistry would be helpful before reading this text. I had to look info up on the internet as I read the book.
Boiler Water Treatment Principles and Practice, Vol. 1, Boiler Basics and Steam-Water Chemistry, Colin Frayne, Chemical Publishing Company, New York, NY, 2002, ISBN 0-8206-0371-6, 0820603716 or 978-0820603711original source: chemical-publishing.com/v/vspfiles/assets/images/pages
%20from%209780820603711_txt.pdf
[2] Quali Chem Technologies, Water & Chemical Specialists, Email: JZajac@QualiChemTech.com, Tel: 800 768-5810, web search 12/4/2011, original source: boilerchemicals.com/Steam-Boilers-Chemicals-s/58.htm
[3] Boiler Water Treatment – Phosphate/Polymer Blend, Accepta, MSDS, web search 12/4/2012, original source: accepta.com/prod_docs/2112-MSDS-phosphate-polymer-boiler-water-treatment.pdf
[4] Boiler Water Treatment Compounds, Spray Chem, web search 01/04/2012, original source: spraychem.com/page/chemicals1.php
[5] Boiler System Chemical Treatment 101, Hayward Gorton Limited, 5 Brigden Gate Halton Hills ON L7G 0A3 T: (905) 693-8595 F: (905) 693-1452 info@haywardgordon.com, web search 12/4/2012, original source: haywardgordon.com/documents/Boiler_Chemical_Feed_Systems_101.pdf

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book 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. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
DUST CONTAMINATION FROM HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
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.
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).
"Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"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.)
Links to our list of additional information on heating system inspection, repair, maintenance
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Where to Check for Leaks on Baseboards, Radiators, or Heating Convectors

Here are some common leak locations on baseboard heating systems

Here are some other common leak locations on hydronic or steam radiators

Frequently Asked Questions (FAQs) about hot water or steam radiator troubleshooting, installation, or repair

Question: repair a pinhole leak in copper baseboard

Reply: solder repairs of small leaks in copper heating baseboard piping

Question: are steam radiator leaks dangerous?

Reply:

Follow-up comment: Harmful chemicals in steam from steam boilers?

Reply: List of common chemicals found in steam boiler water treatment compounds and reference to their MSDS information

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair