Tankless hot water coil leaks & indirect fired water heater coil leaks:

Internal leaks can send boiler pressures up to unsfe levels & can cause TPR valve or relief valve drips or spillage. This article describes how & where these leaks occur, why they are dangerous, and how they can be detected.

How to Detect a Hot Water Coil Leaking Out of the Coil into the Heating Boiler or Indirect Water Heater

When understanding how tankless coil leaks affect a heating boiler we must discuss two different heating boiler types, steam and hot water heat.

Effects of Tankless Coil Leaks on a Hydronic (hot water) Heating Boiler

Because water being heated inside the tankless coil is at building water pressure (typically 20-70 psi) while water inside the boiler itself is at a lower boiler operating pressure (typically 12-18 psi), water entering the boiler from the tankless coil will increase the heating boiler's internal pressure.

• Dripping at the boiler's Temperature/Pressure Relief Valve: You may see a dripping or actually spilling of boiler water at the boiler's temperature/pressure relief valve. Now more than one problem can cause the relief valve to spill .
  
  But if the cause is due to a perforated tankless coil you will also see
  
  Watch out: a dripping pressure/temperature relief valve on any tank or vessel means that a competent diagnosis and repair are needed to avoid the potential of dangerous
  
  BLEVE EXPLOSIONS
  Also
  
  see RELIEF VALVE LEAKS
• Abnormally high pressure inside the heating boiler. Typically a residential heating boiler runs between 12 psi cold and under 30 psi hot.
  
  More than one thing can cause abnormal boiler pressure, such as setting the temperature higher than 200 degF or a control that is malfunctioning, or a water feeder / pressure reducer that is failing, or someone manually over-feeding the boiler.
  
  But if the problem is caused by a tankless coil leak into the heater you can often prove that cause by the following diagnostic steps:
  • Turn off the boiler, let it cool down to room temperature, and then drain water out of the boiler drain sufficient to drop the boiler to its usual cold operating pressure. For taller homes the cold pressure may be higher than 12 psi. For this test it doesn't matter where you stop as long as the cold boiler pressure is set to below the incoming building water supply pressure.
  • Now turn off water supply that feeds the boiler. This will rule out a bad water feeder/pressure reducer valve.
  • Leave the boiler off overnight, or longer if you can. Obviously you can't do this procedure if weather is so cold you can't leave the heat off for a while.
  • Look for a pressure increase in the boiler: At the end of your observation period, 12-24 hours, or sooner if it occurs, look for increasing pressure inside the boiler.
    
    With the boiler off and its own water supply turned off, if you see boiler pressure increasing you can bet the problem is most likely a leaky tankless coil. (Typical building water supply pressure is 40-75 psi, higher than the normal internal operating pressure of a residential heating boiler.
    
    That's high enough to force water out of a perforated tankless coil and into the boiler itself.)
  • Watch Out: When you turn the boiler back on, don't forget to turn on its own water supply as well.

Effects of Tankless Coil Leaks on a Steam Heating Boiler

Some steam heating boilers include a tankless coil used for heating domestic hot water. The tankless coil will be mounted on the steam boiler at a location low enough to ensure that the coil remains immersed in the hot (boiling) water inside the boiler itself.

Because most residential steam heating boilers operate at very low pressures, say 0.5 psi, and because they constantly consume water, you probably won't see the effects of a tankless coil leak into a steam boiler as increased boiler pressure.

Look for abnormally high steam boiler water levels. A leaky tankless coil that is sending water into the steam boiler may never be noticed until the leak becomes severe, because the steam boiler normally consumes water during each heating cycle.

The automagic water feeder on steam boilers so-equipped will simply operate less often. And if the steam boiler uses a manual water feed valve the boiler operator may fail to notice that she has to add water less often or in less quantity than previously.

However when the boiler's heating load is low or is off entirely, such as during warm weather, you will find that the steam boiler water level will reach abnormally high levels, possibly filling the sight glass on the boiler (if an automatic steam boiler water feed valve is installed as is usually the case). Use the same diagnostic steps as for hydronic heating boilers to confirm that the coil is the problem.

Note: a defective automatic water feed valve can also cause excessive water levels in a steam boiler.

See SIGHT GLASS, STEAM BOILER

See WATER FEEDER VALVE, STEAM

We continue below with photographs and details about finding and evaluating and fixing leaks out of the coil.

BOILER LEAKS CORROSION STAINS for a discussion of other types of leaks on heating boilers.

Effects of Heating Coil Leaks on an Indirect Water Heater

Normally a leak in the heating coil of an indirect water heater will show up as increased pressure and leaks at the TPR valve on the hydronic heating boiler that is being used to heat the hot water heating coil inside the indirect water heater's tank.

As long as building supply water pressures remain above the hydronic boiler operating pressures - which is usually the case - the water moves out of the hot water tank and into the heating boiler. You won't see a thing at the indirect water heater.

Watch out: In the unusual event of a double fault: a leak in the hot water coil inside the indirect water heater tank and a loss of building water system pressure, it is possible that unsanitary or non-potable hydronic heating boiler could still leak into the hot water tank.

We explain the normal and also some abnormal directions of water movement

at TANKLESS COIL LEAK DIRECTION IN or OUT

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-09-06 by Byron - diagnose causes of TPR valve leak on indirect water heater system

@inspectapedia.com.moderator,
Thanks. I will start from there.

On 2021-09-06 by inspectapedia.com.moderator (mod)

@Byron,

If you haven't done so, an inexpensive place to start that is also diagnostic is to replace the leaky relief valve.

On 2021-09-06 by Byron

@inspectapedia.com.moderator,
Thanks for your feedback.
Here is my rundown. Sorry for the long stony.

1. I turn OFF the boiler, the psi is 9.

2. Then turn OFF the cold water that feeds to boiler, it’s still at 9. Water is still draining from boiler.

3. Eventually turn OFF the water that feeds to indirect water heater. The psi drops to 0. Hot water stops draining. Should the psi be 0 as normal operations?

4. Turn the water that feeds to Indirect water heater (#3) ON with #1 and 2 OFF, psi goes and stays at 9. Hot water is draining from boiler again.

5. Reverse #4, turn the water that feeds to boiler (#2), with #1, and 3 OFF, psi goes and stays at 9. Hot water is draining from boiler again.

The relief value is leaking based on the observations.

But The water pressure stays at 9 when the boiler is OFF. It’s stable and consistent so it is not a clear signal of broken heating coil in the indirect heater. Not so sure about that..

On 2021-09-05 by inspectapedia.com.moderator (mod)

@Byron,

While it's possible to have two separate faults at once in a system, it's good practice to start with one.

A leak of water out of the indirect heater into the building should be visually obvious;
If that heater leaks water and new makeup water enters from the cold supply line, that would drop the water heater temperature and it would cause the heating boiler - the heat source - to run more-often or even constantly.

A leak of water out of the indirect heater's water tank into its internal heating coil would send higher pressure water (from the water heater) into the heating boiler's lower water pressure system.

If that happens you could see leaks at the heating boiler's relief valve.

To diagnose that you'd turn off the heating boiler and watch its pressure. If its cold pressure climbs abnormally then either there is a tankless coil leak out of the water heater into the heating boiler or the water feed for the boiler itself is defective,

If the cold pressure does not climb but the relief valve is leaking on either device, then the fault is probably the relief valve itself. Replace it.

On 2021-09-05 by Byron - leaks at EcoKing water heater or Viessman boiler

@inspectapedia.com.moderator,

The indirect water heater brand is EcoKing. The model number is ISSW200 (Glass Lined Indirect Storage Tanks).

The Boiler brand is Viessman, model Vitodens 100-W. I believe the relief value of boiler spilled, and suspect the indirect water heater is leaking, so try to find out the causes of the continuous hot water drainage from the boiler (see red circle in the attached photo)
Thanks!

On 2021-09-04 by inspectapedia.com.moderator (mod)

@Byron,

It would be helpful to have a better understanding of what you have installed, by product, brand, model, maybe a sketch;

TO me an "indirect water heater" is simply a tank whose water is heated by an internal coil; hot water from a heating boiler circulates inside that coil and the coil is immersed in the indirect water heater's supply of hot water.

What's spilling? A relief valve on your heater, a relief valve on your indirect hot water tank itself, or something else?

On 2021-09-04 by Byron

@inspectapedia.com.moderator,
Update. Last night, I left the water supply to the indirect water heater ON, and both boiler and water supply that feeds the boiler OFF. The psi stays at 9. The hot water was continuously drained out of the boiler.

After 20 minutes, the drained water started to get cooler. When I came back 8 hours later, the psi is still 9, and the boiler drained water is at tap water temperate.
After turning both boiler and water supply that feeds the boiler ON, the boiler started boiling at 90F, and stopped at 170F. The psi stayed at 9 for all time.
Thanks.

On 2021-09-04 by inspectapedia.com.moderator (mod)

@Byron,

That sounds like a good Next Step. Do keep me posted.

On 2021-09-04 by Byron

@inspectapedia.com.moderator, Thanks for your quick feedback. I checked the plumbing connections, and they are fine. I checked the relief value and it’s not lifted. When I lifted it, the water was drained, and the psi of boiler dropped to zero. The psi returned to 9 when I released the lift.

When the indirect water heater is asking for heat, the boiler started boiling and its temperature dropped from 170F to 110F in a second, and gradually increased to 170F while boiling. It turned back to 160F right after boiling and climbed back to 170F in 5 minutes. The temperature stayed at 170F until the next boiling.

Another weird reading found is the psi. The boiler psi stays at 9 before, during, and after boiling.

I am not sure if it’s related but I also suspect the indirect water heater is leaking that may be one of the causes of water draining continuously. It’s only 5 years old but it’s not fine.
For example, when I turned off both pipe shut off values of coil inlet and outlet connected to the indirect water heater. The boiler psi dropped to 6. The psi goes back to 9 when it turned them on.

I did another test. When I turned OFF boiler, then OFF the water supply that feeds the boiler, the boiler psi stays at 9. Then I turned OFF the water supply to the indirect water heater 5 minutes later, the boiler psi dropped to 0. After 10 minutes, the water draining issue stopped. I turned it back ON in 10 minutes, the boiler drained water to the black pipe again and the boiler psi goes back to 9 in 15 minutes.

I will leave the water supply to the indirect water heater ON, and both boiler and water supply that feeds the boiler OFF for a night, and check the boiler psi in the morning.
Thanks.

On 2021-09-03 by inspectapedia.com.moderator (mod)

@inspectapedia.com.moderator, and Byron:

If you don't have it, see this

• VITRODENS 100 SERIES GAS BOILER MANUAL (APPLICATION GUIDE) [PDF]
  

On 2021-09-03 by byron: Vitodens 100-@ boiler is draining hot water to the black drainage pipe continuously, 24 hours a day.

Re-posting comment without improper advertising link

We deleted your link to Kingman a that is an advertisement for glass lined indirect storage hot water tanks and doesn't appear to have to do with your Vitrodens 100 ??? boiler that you say is leaking contuously.

Byron said:

Hello. May I ask for opinion? I really need your help. My Vitodens 100-@ boiler is draining hot water to the black drainage pipe continuously, 24 hours a day. It's nonstop. It's summertime so the heater is off.

The boiler is burning water for my indirect water heater every 30 minutes even though nobody is using hot water at midnight. I checked The pressure relief value and it's not working.

The trick part is to determine whether my indirect water heater’s coil (EcoKing ISSW200) is leaking.

[link deleted]

Before turning off the boiler and off water supply that feeds the boiler as your website, I checked the status of the boiler. The boiler psi is around 9 when the boiler is ON and idle without burning water. The temperature is around 170F. The psi is too low and temperature is too high to me. I expect it’s about 12 psi and 145F when it’s idle. What are the possible causes and how should I test the leaking if it’s abnormal to begin with?

Thanks in advance.


Moderator reply:

@Byron,

From your description, it sounds as if either the boiler's controls or thermostat are not properly wired or the control is not working properly.

This heater comes with a "lifetime warranty" so you will want to contact the manufacturer

Viessmann Manufacturing Company Inc. 750 McMurray Road
Waterloo ON, N2V 2G5, Canada
Phone: 519-885-6300 Toll Free: 800-387-7373
www.viessmann.ca

But before doing so,

Check by opening the boiler cover to see if there is an obvious point of leakage such as a poor plumbing connection - just to safe us both from embarrassment.

Check that no one lifted and left open the test lever on the relief valve.

Check the temperature and pressure while the boiler is on and leaking, and compare those to the pressure and temperature data on the tag attached to the pressure relief valve. If the temperature and pressure are well below those at which the valve is supposed to open, then it sounds if the problem is NOT over-pressure or over temperature (which should cause the relief valve to spill).

On 2017-05-19 by (mod)

It is potentially dangerous in that over-pressurizing a boiler (or flooding a steam boiler) can spill the relief valve, ultimately clogging it and thus risking a BLEVE (explosion) - search InspectApedia for BLEVE EXPLOSION to see details. Even before that more-remote catastrophe, flooding the boiler leads to loss of heat.

Why not simply shut off the tankless coil - thus confirming the leak. Then if it's confirmed, either replace it or leave it off and use an alternative hot water source. It's not something that can be "tolerated", and it is something that is likely to get worse, possibly suddenly.

On 2017-05-18 by Phil

My HVAC repair man thinks I have a tiny leak in a coil in my tankless hot water heater. It is an Everhot All Copper tank #16, red round tank mounted horizontally on the side of my old National boiler.
The only indication of any leak is that the water creeps up in the sight glass. We have replaced many rusted pipes, changed valves.

Is this dangerous, and is it a huge problem now to remove this and to invest in a separate water tank. I am discouraged at this point.

Thank you.

...

Continue reading  at REPAIR OPTIONS for TANKLESS COIL LEAKS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• INDIRECT WATER HEATER COIL LEAKS INTO the BOILER
• RELIEF VALVE LEAKS
• TANKLESS COIL / HOT WATER COIL LEAKS
  • TANKLESS COIL EXTERNAL LEAK SPOTS
  • TANKLESS COIL EXTERNAL LEAK EVALUATION
  • TANKLESS COIL RUST TYPES: SUPERFICIAL vs EXFOLIATION
  • TANKLESS COIL INTERNAL LEAKS INTO the BOILER
  • INDIRECT WATER HEATER COIL LEAKS INTO the BOILER
  • TANKLESS COIL LEAK DIRECTION IN or OUT
  • EVIDENCE of TANKLESS INTERNAL COIL LEAK INTO BOILER / WATER TANK
  • REPAIR OPTIONS for TANKLESS COIL LEAKS

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EVIDENCE of TANKLESS INTERNAL COIL LEAK INTO BOILER / WATER TANK at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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