Tankless hot water coil leaks, corrosion, & repair procedures:
In this article series we explain how to spot, evaluate, and repair leaks at the tankless coil used on heating boilers to provide domestic hot water or leaks in the hot water heating coil used on indirect-fired water heaters.
Leaks can occur at a tankless coil where it is mounted to the top or side of a heating boiler or water tank (if an indirect water heater is in use), at fittings connecting hot and cold water piping to the coil, and more subtle leaks can occur inside the boiler or water tank - leading to excessive boiler pressure and to dangerous TPR relief valve leaks.
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This article provides a guide to recognizing and evaluating leaky boilers. How to evaluate the severity of leaks at a hot water tankless coil. Why leaks at a tankless coil can ruin a heating boiler. How to inspect repair leaks at tankless coils on heating boilers.
We address these tankless coil leak questions: When is a tankless coil leak or indirect water heater coil leak repairable? Leaks at the tankless coil mounting plate can often be repaired if caught early.
Severe rust at a tankless coil mounting plate means tankless coil replacement is impossible and the boiler may be ruined. When is boiler replacement necessary? How to diagnose a tankless coil that leaks into the heating boiler.
[Click to enlarge any image]
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.
Leaks at the heating boiler - coil: A leak at any of these points will not normally show up as water on the boiler or on the indirect water heater or on the floor around the boiler or around the indirect fired water heater. That's because the boiler is normally hot all of the time. Water leaking at any of these locations on a heating boiler will rapidly evaporate.
Leaks at the indirect fired water heater: Water leaking out of the coil mounting plate or fittings on an indirect fired water heater may appear as a puddle on the floor or it may be absorbed in water heater insulation where it is evaporated - for a time, until the leak gets bad-enough to show up externally.
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.
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.
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.
Our next photos show how prolonged leaks at the coil face plate mounting gasket can destroy a heating boiler.
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.
To permit faster loading and more writing space we've moved the remaining topics of this original article into the following illustrated discussions:
This topic has moved to a separate article.
See TANKLESS COIL INTERNAL LEAKS INTO the BOILER
This topic was moved to a separate article. Please
see INDIRECT WATER HEATER COIL LEAKS INTO the BOILER
Topic moved to a separate article. Please
see TANKLESS COIL LEAK DIRECTION IN or OUT
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see EVIDENCE of TANKLESS INTERNAL COIL LEAK INTO BOILER / WATER TANK
see REPAIR OPTIONS for TANKLESS COIL LEAKS for a discussion of leaks in both tankless coils on heating boilers and the heating coil used on indirect-fired water heaters.
Continue reading at TANKLESS COIL INTERNAL LEAKS INTO the BOILER or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see RELIEF VALVE LEAKS
Or see BOILER LEAKS CORROSION STAINS for a discussion of other leaks on heating boilers.
Or see WATER HEATER LEAK REPAIR
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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
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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