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 How to Diagnose, Evaluate & Repair Leaks at a Tankless Coil on a Heating Boiler
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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. 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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Leaks at tankless coils: location, cause, detection, cure
Leaks at tankless coils used to produce domestic hot water occur at the following locations:
- 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
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 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.
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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 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.
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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.
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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) about leaks at tankless hot water coils: cause, diagnosis, repair advice
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. - rwrusso@msn.com 9/6/11
Reply:
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;
You seem to be asking about a stand alone tankless water heater, not part of a home heating boiler. Those are discussed separately under
TANKLESS WATER HEATERS (article link at page top).
The heat exchanger coil in those units is replaceable too; the heater shell can usually remain attached to the building but the cover is removed and a bit of disassembly will be required.
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.
Then I thought of how to fix it the cheapest way. It did cost me $5.00 to fix it.
Here is what you do:
1- Shut off the boiler electrical switch and Close all valves around the boiler.
2- Drain the boiler from any water left.
3- Fill the coil (From any possible water inlet to the boiler) with Radiator Heavy Duty Stop Leak (Find it in any auto supply store).
4- Add about one liter warm water to the same inlet.
5- Switch on the boiler and let it run till the thermostat shut the fire off. The higher temp setting the better result you’ll get.
6-Shut off the boilers electrical switch and Let it cool down for 20 minutes.
7- Repeat the same twice more.
8- Now open the valves and let the boiler filled with water.
8-Some water may come out through expanding the cold water when it is heated for the first time only but the coil will be sealed for many years to come.
Repeat it after few years when it happened again.
You can use the same to stop auto radiator small leaks.
Sorry plummers. Enjoy it home owners.... :)
Talal Mikhail 4/1/12
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.
Leaks into the boiler: a tankless coil may develop a leak in the finned copper tubing that is inserted into the heating boiler interior. Such a leak will send household water supply into the boiler, causing excessive pressures in the boiler, perhaps showing up as a leaky boiler pressure / temperature relief valve, or as abnormally high pressure on the boiler pressure gauge. This is the sort of leak the reader below is describing. W
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.
The second type of tankless coil leak, and the one illustrated on the page above, is a leak of heating boiler water out of the boiler around the tankless coil mounting plate or bolts.
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.
Old timers used to run oatmeal through the car radiator, and there is a similar lore of magic leak fixes that were applied to cast iron boiler leaks. But for a corroded, leaky tankless coil around its mounts, you have to catch the leak early, remove the coil, clean up the mating surfaces, install a new gasket and reassemble. If you wait long enough, it's new boiler time.
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