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Tankless hot water coil leaks, corrosion, & repair procedures: This article explains leaks at Tankless Coils on heating boilers: a guide diagnosis, evaluation, & repair of leaks at tankless coils used for making hot water. Leaks can 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 these leaks at a tankless coil can be repaired without serious damage to the heating boiler. Left alone these same leaks, particularly at the tankless coil mounting plate 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.

We introduce tankless coils as a source for domestic hot water, and we explain how they work at TANKLESS COILS. We discuss how to improve hot water quantity at HOT WATER IMPROVEMENT. 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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Leaks at tankless coils occur at the following points

1. At the tankless coil face tapping for mounting a temperature sensor (bottom center pipe shown in this photo, leading to a boiler combination control).
   
   
2. At the tankless coil face tapping for the incoming cold water or outgoing hot water pipe (the two copper pipes shown in this photo)
   
   
3. 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

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.

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 at the bottom of the tankless coil mounting plate and to the right of the largter white leak stain? This tankless coil appears to 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.

Photo Guide to Severe Tankless Coil Leak & Rust Damage

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.

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.

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.

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TANKLESS COILS
  AQUASTAT CONTROL Functions
  Clogged Pipes / Tankless Coil De-Scale
  MIXING / ANTI-SCALD VALVES
  Tankless Coil Conversions
  Tankless Coil Leaks
  Tankless Coil Hot Water Increase

MIXING / ANTI-SCALD VALVES on tankless coils, why and how
BOILER LEAKS CORROSION STAINS for a discussion of leaks on heating boilers.
HOT WATER IMPROVEMENT for a discussion of how to get more hot water from a tankless coil.
WATER SOFTENERS & CONDITIONERS for a discussion of how to install and use a water softener to avoid mineral clogging of the hot water supply piping and equipment

• 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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