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Tankless hot water coil leaks, corrosion, & repair procedures: Here we explain how to spot, evaluate, and repair leaks at the tankless coil used on heating boilers to provide domestic hot water. Leaks can occur at a tankless coil where it is mounted to the top or side of a heating boiler, at fittings connecting hot and cold water piping to the coil, and more subtle leaks can occur inside the boiler - leading to excessive boiler pressure and relief valve leaks.
The home page for tankless coils as a source for domestic hot water and an explanation of how they work is at TANKLESS COILS.
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[Click to enlarge any image]
Common locations of leaks at or around tankless coils on the heating boiler that leak out of the coil or boiler
Boiler leaks out 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. You may not see water (the boiler is hot, after all) but you'll see mineral deposits and crud or even crud and rust build-up at the leak source and below it.
Watch out: aught 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.
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.
How to Evaluate a Leak at a Tankless Coil on a Heating Boiler
Young leaks at a tankless coil can be repaired
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.
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
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.
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.
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.
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.
Severe 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.
Leaks from a tankless coil into the heating boiler will raise boiler pressure
Watch out for this second and more tricky to spot tankless coil leak. Corrosive water, usage, repeated acid cleanout of a mineral-clogged tankless coil, or other wear and tear can cause the finned copper tubing of the tankless coil to leak water at house pressure into the interior of the heating boiler itself.
Take a look at that pile of tankless coils in our photo (left). When we found all three of these near the heating boiler in a home we knew that there had been a history of trouble with leaky tankless coils. You can see in the photo (click to enlarge) that there is virtually no rust or corrosion around the coil mounting plate.
You would never spot this leak by just looking at the boiler externally. But each of the three coils has some funny-looking brass-colored discoloration around the finned tubing near the mounting plate, in the first three coil turns. That's just where you might find thin coil tubing and perforations due to one of the causes we list below.
Causes of internal leaks in a tankless coil - leaks into the boiler
Our photo (left) illustrates leaks around the tankless coil (top center on this boiler) mounted so that little of the coil itself is visible - it's hidden by the blue BlueRay II boiler mounting jacket. But the rust stains below the boil make the leak obvious. Also see BLUERAY Recall
How to spot and diagnose a tankless coil that is leaking into the heating boiler
We continue below with photographs and details about finding and evaluating and fixing leaks out of the coil.
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 above 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.
Also see BOILER LEAKS CORROSION STAINS for a discussion of leaks on heating boilers.
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Frequently Asked Questions (FAQs)
Question: can a leak be repaired with a tankless heater still attached to the wall?
can a leak normally be repaired with the unit still attached to the wall> Does one remove the pipes inside of the heat exchange of the tankless water heater? Are there parts for such items. My unit is Nakagki. Small water leak so far. - firstname.lastname@example.org 9/6/11
The type of tankless coil we discuss here is a part that inserts into a heating boiler; It can't be repaired if it's leaking, but the entire assembly can be replaced; It's a significant job - the boiler has to be drained;
Question: Home Depot "experts" said that repairing a tankless coil leak is impossible - but I used radiator heavy duty stop-leak from an auto parts store
went to home Depot asking if there is any way to fix my boiler coil’s water leak. They looked at me like an idiot. No way can you fix the coil, they said. You must change it.
Reply: Bad repair - you risk poisoning building occupants; don't try oatmeal in the tankless coil either.
Thanks for this interesting, if questionable repair idea for leaky tankless coils. It needs some clarification.
e are not sure what the effect may be on the heating boiler, circulator pumps, zone valves, relief valve, of the passage of any stop leak compound into those components through the leaky coil before the leak stops - those may be harmful. Auto radiator stop leak is not designed for this circumstance. It might work but it leaves me a little worried.
This leak, as you can see in our photos, destroys the boiler if it is not found soon enough, and destroys the tankless coil mounting plate - an integral part of the assembly. That's why the Home Depot rep was dead right when he said "replace the coil" - she or he was thinking of this common leak. Auto radiator "stop-leak" products won't fix this problem, and in fact running a stopleak product through the coil is irrelevant because that's not where the leak is found.
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