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How to Diagnose, Evaluate & Repair Leaks at a Tankless Coil on a Heating Boiler
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Leaks at Tankless Coils on heating boilers: a guide to recognizing and evaluating leaky boilers
How to inspect repair leaks on heating boilers
When is a leak repairable? When is boiler replacement necessary?
Questions & answers about the cause & repair of leaks at tankless coils on boilers

Repair leaky tankless coil on heating boiler: Here we explain Leaks at Tankless Coils on heating boilers: a guide diagnosis, evaluation, & repair of leaks at tankless coils.

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We introduce tankless coils as a source for domestic hot water, and we explain how they work at TANKLESS COILS. Here we explain leaks that occur at a tankless coil where it is mounted to the top or side of a heating boiler. Boiler leaks at a tankless coil mounting plate or at the pipe fittings that pass through the coil mounting plate are a common defect on heating boilers, both steel and cast iron units.

Caught and repaired early, leaks at a tankless coil used to make hot water can be repaired without serious consequence. Left alone these same leaks can completely destroy the heating boiler. Deciding how badly a heating boiler has been damaged by leaks is tricky, controversial, and important since both safety and big cost concerns are involved.

Leaks at tankless coils occur at the following points

At the tankless coil face tapping for mounting a temperature sensor (bottom center pipe shown in this photo, leading to a boiler combination control).
At the tankless coil face tapping for the incoming cold water or outgoing hot water pipe (the two copper pipes shown in this photo)
At the tankless coil mounting plate where it is bolted to the face of the heating boiler (the round and rusty steel face shown in this photo).

A leak at any of these points will not normally show up as water on the boiler or on the floor around the boiler.

That's because the boiler is normally hot all of the time. Water leaking at any of these locations will rapidly evaporate.

What evidence of leaks will we observe at a boiler with leaks at the tankless coil?

White or other mineral salts left behind from evaporating leaky water, at and below the point of leakage, often staining the face of the boiler, such as we show in the photograph above. Even without close inspection one can observe white leak stains below the round black tankless coil plate and running down the face of the boiler in this installation.

Rust or corrosion at the point of leak, such as the flaking exfoliating and badly rusted tankless coil we show in our photograph at left. .

A leak that has produced rust like this might mean that the tankless coil unit needs to be replaced, or worse, that the boiler has been so damaged by rust that it is beyond repair.

In the next section of this article we discuss how to evaluate leaks on heating boilers at a tankless coil

How to Evaluate a Leak at a Tankless Coil on a Heating Boiler

Young leaks at a tankless coil can be repaired

If a leak is found in time, that is, before severe rusting and exfoliating or flaking rust have occurred, it should be possible to disassemble, clean, seal, and re-assemble the parts.

In our photo at left we'd probably call this a "middle-aged" leak rather than a "young leak" because the white mineral salt deposit you see below the tankless coil on the face of the boiler is pretty thick. But it's possible that this tankless coil leak can be repaired. A closer inspection is needed.

Leaks at piping connections on the tankless coil itself can be repaired without removing the whole coil assembly from the boiler.
Leaks at the tankless coil mounting plate will require that the boiler be shut down, drained, and water piping connections cut or opened at the coil so that the coil assembly can be removed. If inspection shows that the coil face and boiler mating face are un-damaged, the mounting gasket is replaced, sealed, and the coil reassembled to the boiler.

This may seem an odious task, since it means you'll need to shut down the boiler and also domestic hot water, and boiler water and piping water may need to be drained or partly drained in order to make this repair.

But you should make this repair as soon as possible.

Old leaks at a tankless coil may require boiler replacement

If a leak is not found in time, or if no one was willing to repair a young leak, the cost is likely to be very high.

Leaks at pipe connect on a tankless coil (C) Daniel Friedman

Leaks at piping connections through the face plate of the tankless coil, if they have progressed for a long time, will have caused so much corrosion that disassembly and repair of the coil is impossible.

The good news is that leaks at this location only destroy the tankless coil itself and are less likely to destroy the whole heating boiler. The coil will need to be removed and replaced.

The white deposits on the face of this tankless coil appear to originate at a pipe connection at the coil face (top center of the photo); but notice that second leak trace to the right of the white one?

This tankless coil may also be leaking at its gasket. Our next photos show how prolonged leaks at the coil face plate mounting gasket can destroy a heating boiler.

Leaks at the tankless coil mounting plate, if they have progressed for a long time, will have caused damage to the coil mounting plate.

But much worse, the mounting surface on the boiler will also be damaged. If the boiler surface has been damaged it may be impossible to mount a replacement tankless coil without continuing leakage.

It is technically possible to perform a repair to such a boiler by welding on a new coil mounting surface, but the welder is not going to be very interested in performing such a small but time consuming repair, and knowing that the alternative to her welding service is a whole boiler replacement, the price for the welding job may be rather high.

Which Tankless Coil Leaks & Boiler Leaks Can Be Repaired and When is the Boiler Ruined?

Rusty tankless coil face plate and boiler surface: Look closely at the coil mounting plate and the boiler mating surface to see just where the rust and exfoliating have occurred.

In our photo at left, this boiler, in Wappingers Falls, NY, was beyond repair. Leaks at the tankless coil had badly rusted the coil face plate, the boiler face, and even the boiler jacket.

In most cases a leak at the coil mounting plate, left unattended, will have badly rusted both surfaces and the boiler is likely to be beyond repair.

Rusty tankless coil face plate, possibly salvageable: But in some cases the rust and flaking may be occurring on the outer face of the tankless coil mounting plate, and there is a chance that the coil can be removed and replaced. In the photo above we show here we see severe flaking exfoliating rust on the outer face of the tankless coil face plate.

Boiler mounting surface for tankless coil

In this photo we can see that the inner mating surface of the boiler, the surface to which the tankless coil face plate has to mate, looks as if it might be ok.

In this case it seems worth trying to remove the tankless coil to see just what the situation really is.

Replacement of the coil and saving the boiler might be possible in this case.

Rusty tankless coil bolts & Studs: Of course a related problem is that the coil mounting bolts and studs may be so badly rusted that they will be broken during removal of the coil. It's possible to drill, tap, and restore broken coil mounting studs, but lots of work and cost are involved.

That's why your plumber will be reluctant to promise that a boiler can be saved even when it appears worth making an attempt to do so.

Also see BOILER LEAKS CORROSION STAINS for a discussion of leaks on heating boilers.

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Questions & answers about the cause & repair of leaks at tankless coils on boilers

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HOT WATER HEATERS
HOT WATER IMPROVEMENTS
HOT WATER QUANTITY IMPROVEMENT

TANKLESS COILS
  AQUASTAT CONTROL Functions
  Clogged Piping / Tankless Coil & Hot Water Flow
  MIXING / ANTI-SCALD VALVES
  Tankless Coil Leaks
  Tankless Coil Hot Water Increase
  Tankless Coil Conversions
TOILET FLUSHOMETER VALVES
TOILET INSTALLATION PROCEDURE
TOILET OVERFLOW EMERGENCY
ODORS GASES SMELLS, DIAGNOSIS & CURE
ODORS IN WATER
OIL FIRED WATER HEATERS
MIXING / ANTI-SCALD VALVES
RANGE BOILERS
RELIEF VALVES - TP VALVES
SOLAR HOT WATER HEATERS
WATER HEATERS
AGE of WATER HEATERS
ALTERNATIVE HOT WATER SOURCES
  Electric Shower Heaters
  High Efficiency Water Heaters
  Indirect-fired Water Heaters
  Instantaneous Water Heaters
  Multiple water heaters in parallel
  Multiple water heaters in series
  Range Boiler Water Heaters
  Side Arm Coil Water Heaters
  Solar Water Heaters
  Tankless Coil for Hot Water
  Tankless Water Heaters
ANODES & DIP TUBES on WATER HEATERS
ELECTRIC WATER HEATERS
FLOODED WATER HEATER REPAIR
GAS FIRED WATER HEATERS
HOT WATER IMPROVEMENTS
HOT WATER QUANTITY IMPROVEMENT
INDIRECT FIRED WATER HEATERS
WATER HEATER NOISES
WATER HEATER PROPERTIES
WATER HEATER SCALE - De-Liming Procedure
WATER HEATER SCALE PREVENTION
WATER PRESSURE LOSS DIAGNOSIS & REPAIR
WATER PRESSURE PROBLEM DIAGNOSIS TABLE

WATER PRESSURE & FLOW MEASUREMENT

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.

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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
Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
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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.
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Leaks at tankless coils occur at the following points

What evidence of leaks will we observe at a boiler with leaks at the tankless coil?

How to Evaluate a Leak at a Tankless Coil on a Heating Boiler

Young leaks at a tankless coil can be repaired

Old leaks at a tankless coil may require boiler replacement

Which Tankless Coil Leaks & Boiler Leaks Can Be Repaired and When is the Boiler Ruined?

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

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