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Hot water heating sytsem leak diagnosis & repair; here we explain how to find the location of hidden leaks in or on heating boilers, hot water heat piping, baseboards, radiators, convectors, or radiant heat floors or ceilings.

Readers should also see BOILER LEAKS CORROSION STAINS where we provide a catalog of places where leaks often occur on hot water heating systems. This website answers most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect residential heating systems to inform home owners, buyers, and home inspectors of common heating system defects.

The photograph at page top shows that a heating convector recessed into the wall had been leaking into the wall structure for a long time. The leak was discovered by removing the convector cover for direct inspection. We could also see evidence of this leak by inspecting for water stains or damage at the building sills in the basement below.

It is important to recognize and accurately report the significance of rust like this on any heating boiler. We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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Tips for Finding Leaks on Hot Water Boilers or in Hot Water Heating Distribution Piping

Most modern heating boilers include an automatic water makeup valve that combines pressure reduction (to 12 psi cold on the boiler side of the valve) with automatically makeup water if the boiler pressure drops below that point. Details are at Water Feeder Valves, Hydronic Boiler.

How Do I Know if my Heating Boiler is Leaking?

A small water leak in a hot water heating system (hydronic heat) will eventually cause pressure loss in the system, but you may never notice this problem. Leaks on hot water heating systems are likely to occur, or to leak more rapidly when the heating system is hot (at higher pressure) than when it's cool.

The pressure drop from a small heating system water leak may be occurring over a long time, months or longer, and because the leaked-water may simply dry out on the hot heating piping where it is occurring you may never see a wet spot on a floor, wall, or ceiling below the leak.

Our photo (left) shows the mineral build-up at a leaky air purge vent on a hot water heating system. Notice also those white leak stains on the boiler top itself.

How Do I Find Leaks on Hot Water Heating Systems?

To detect a small leak in a hydronic heating system we have had some success with these measures:

• Inspect the entire hot water heating system, all hot water piping, the boiler, controls, valves, circulator pumps, piping elbows and piping, baseboards, radiators, air bleeders, etc. for evidence of mineral build-up that indicates a leak. If you have not already done so, take a look at BOILER LEAKS CORROSION STAINS where we provide a catalog of places where leaks often occur on hot water heating systems.
• Temporarily turn off the water supply into the heating boiler and monitor the cold pressure of the system when it has shut down. If you see that the cold pressure, shown on your boiler's gauge is slowly dropping, especially if it falls by several psi over weeks or longer (for example over summer months when the boiler is shut down) there is probably a small leak somewhere.
  
  Remember that leaks are faster when the boiler is hot, but reading the "hot" pressure on the boiler won't help in this instance.
• For radiant floor or ceiling heating systems that use hot water tubing, borrow or rent an infra red scanner or thermography camera to look for hot abnormal hot areas that spread out around a hidden leak - for example in a concrete floor slab. You'll find that you can easily spot the routing of the hot water tubing; look for an area where the heat spreads out more widely than at other tubing lengths. See RADIANT HEAT.

Questions & Answers regarding this article

Questions & answers about leaks on hot water heating systems: how to find and fix leaks

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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.

BOILERS, HEATING

BOILER LEAKS CORROSION STAINS
BOILER LEAKS, HOW TO LOCATE
BOILER NOISE SMOKE ODORS
BOILER OPERATING PROBLEMS
  Types of Boiler Defects
  Air-bound radiators, baseboards, boilers
  COMBUSTION AIR DEFECTS
  Diagnose Loss of Heat
  Diagnose Oil Heat Noises
  GAS BURNER Flame & Noise Defects
  OIL BURNER NOISE SMOKE ODORS
  OIL BURNER SOOT & PUFFBACKS
  Heat Won't Turn Off - Stop Unwanted Heat
  Heating Malfunctions & Implications
  Heating Defects & Implications
  Leaks at Heating Boilers
BOILER OPERATION DETAILS
BOILER PRESSURE & TEMPERATURE SETTINGS

CONDENSING BOILERS/FURNACES
CONDENSING BOILERS/FURNACES DAMAGE

DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE

FLOODED HEATING EQUIPMENT REPAIR
FLOODED WATER HEATER REPAIR

HEATING SYSTEM INSPECT DIAGNOSE REPAIR
HEATING SYSTEM INSPECTION DETAILS
HEATING SYSTEM NOISES
HEATING SYSTEM SERVICE & MAINTENANCE

HEATING SYSTEM TYPES

RELIEF VALVES - TP Valves on Boilers
RELIEF VALVES - STEAM TP VALVES
RELIEF VALVES - Water Heaters
RELIEF VALVES - Water Tanks

WATER HEATERS

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.

• 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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