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Photograph of severe rust damage on a steel heating boilerHow to Diagnose & Fix Leaks at Heating Boilers

Heating boiler leak repairs:

Here we explain how to detect, diagnose, find, & evaluate leaks in or on hydronic heating boilers with focus on residential heating boilers, including leaks leading to loss of heat, heating boiler noises, leaks, odors, or smoke, and high heating costs.

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How to Evaluate Heating Boiler Leaks & Corrosion

Tankless coil leak (C) Daniel Friedman

Our photograph at page top shows severe rust at the tankless coil on a steel heating boiler - this boiler may be beyond repair even though the rest of the unit looks pretty good.

When a tankless coil-mounting surface on the boiler itself is severely rusted it may be impossible to get an adequate seal when bolting on a new hot water coil, making it necessary to replace the entire heating boiler.

See TANKLESS COIL / HOT WATER COIL LEAKS for more about this device.

[Click to enlarge any image]

It is important to recognize and accurately report the significance of rust like this on any heating boiler. We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

Even significant boiler water leaks at a tankless coil (left and at page top) may never show up on the building floor as a wet spot, leading an owner to ignore a condition that can lead to very expensive damage.

When observing evidence of leaks on a heating boiler, keep these points in mind:

Below: white and yellow effloresence (mineral salts) left behind by a small to modest leak somewhere above on this 1990s Weil McLain gas boiler were found at the under-side of the heat exchanger during a careful boiler inspection and tune up job on this boiler in Two Harbors, Minnesota in 2022.

Under-side of cast iron Weil McLain gas boiler in Two Harbors shows mineral salts - signs of leakage from above (C) InspectApedia.com Amy Church

This evidence of boiler leakage was not, in the opinion of the boiler inspection technician, a reason to condemn the boiler, but it's a warning to look for and fix any leaks above.

Below is a repair: installation of a new water feedline, on an old cast-iron boiler. The service technicians were able to remove an old rusty water feeder and install a new one.

Had the more-complete condition of the boiler been understood by the building owner at the time she might have opted to skip this water feed repair and replace this old Weil McLain steam boiler, because as we show later, within a short time it was found to be beyond further repair.

Repair that was possible: repalcing a water feed pipe on an old Weil McLain Steam Boiler  (C) Daniel Friedman at InspectApedia.com Lukacher

Boiler section leak (C) Daniel Friedman


Diagnostic Questions Help Evaluate Water Leaks on Heating Boilers

Leaky steam boiler: damage assessment procedure decides if the boiler should and can be repaired (C) Daniel Friedman at InspectApedia.com ...

Above and below: a leaking steam boiler at a Poughkeepsie,

Leaky steam boiler: damage assessment procedure decides if the boiler should and can be repaired (C) Daniel Friedman at InspectApedia.com

New York Home in 2021. How bad were these leaks? Was this boiler repairable?

Leaky steam boiler: damage assessment procedure decides if the boiler should and can be repaired (C) Daniel Friedman at InspectApedia.com

Was the boiler repairable?

1. Is the existing corrosion and rust so bad that there is a significant chance that trying to disassemble the parts will lead to a total failure and need to replace the whole boiler?

If not, give it a shot. With appropriate and due warnings.

Below: with the covers off of the Weil McLain steam boiler shown above, we see that the cast iron sections and the bolt holding them together are rusted nearly completely-through. This boiler was beyond repair.

Catastroic leaks, long ignored, destroyed this oil fired steam boiler in New York (C) Daniel Friedman at InspectApedia.com

When do we let the boiler alone and ignore the leak ? What's the cost? What are the risks?

2. If the parts are so corroded that a replacement of the whole boiler might be required, what's the cost of ignoring the problem until we see water on the floor?

Answer, as was experienced by the homeowner of the boiler we show in our photos.

2.a. The leaky corroded heating boiler is most-likely to fail when it's working the hardest, hottest, under longest periods of highest pressure: during the peak of the heating season on the coldest days of the year.

That's what this homeowner experienced. The result was a boiler that was so leaky and deteriorated what when the homeowner called for emergency service the heating tech took one quick look at the boiler and shut it down for safety, worrying that the whole unit could explode or burst or flood the home's basement. Deeming the unit unsafe he red-tagged it.

The homeowner was then without heat for several days until the heating service company could locate, obtain, and bring a new boiler to the site for a replacement job.

2.b.There was a further risk that the home's basement could be flooded by leakage - mitigated if the service company or homeowner were able to turn off the water supply to the now shut-down and red-tagged boiler.

There were additional costs as well. Because the boiler had to be replaced on an "emergency" basis, the boiler and its installation cost more than it might had it been replaced at a more-opportune time, such as mid-summer.

Our first photo, above showed how the cast-iron sides of the boiler were rusted through.

Our second failed leaky boiler photo below shows that a heavy steel pipe (the condensate return port) on the boiler's bottom-back was rusted so thin that not only was it leaking, but it was easily broken away by simple hand pressure when the repair crew came to the job.

This boiler was beyond repair by the time the homeowner called for repair service.

Sometimes a leaky gasket at a tankless coil can be replaced by removing the coil, cleaning the surfaces, and installing a new gasket + sealer.

Catastroic leaks, long ignored, destroyed this oil fired steam boiler in New York (C) Daniel Friedman at InspectApedia.com

Our photo above, of the same failed leaky boiler whose cast iron sides were rusted through (above) shows that the steel pipe for the condensate return at the boiler's bottom-back was rusted so thin that not only was it leaking, but it was easily broken away by simple hand pressure when the repair crew came to the job.

The condensate line return pipe and port leak, the main cause of water on the floor at this oil fired steam boiler, were rusted through - again, beyond repair.

5 Key Questions about Rust on a Heating Boiler or Water Heater

When you see thick exfoliating rust and corrosion on a heating boiler or calorifier, even before there's water on the floor, there are some critical questions to answer:

  1. Where is the rust?

    Only on the part to be removed or also on the mating surfaces of the boiler?
  2. How bad is the rust?

    Is it surface rust - the parts can probably be removed successfully, or is there thick exfoliating flaking rust - the parts may meet with disaster on trying to execute the repair
  3. What are the surrounding conditions?

    Is the current weather very cold? Can the building and its occupants be without heat for a time?

    What are the potential costs and risks of a more-serious leak or of a loss of heat that may occur if the repair is deferred?
  4. Can we wait & would it be better to wait for warmer weather to perform the repair?

Bottom line: if you can fix a leak in time to avoid destroying the boiler, it's worth giving that a shot.

 

A Catalog of Common Heating System Leak Points - Where to Watch for Heating System Leaks

Leaky circulator pump (C) Daniel FriedmanNote: the following catalog of common places where you may find leaks on a hot water heating system boiler or its components is arranged alphabetically. Some of these leaks, such as at TPR valves, are dangerous and require urgent attention or even system shut-down.

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2013-03-13 - by (mod) -

You don't say how hot water is being made.

You might try looking at the simple diagnostic "no hot water" steps at

HOT WATER PRESSURE LOSS

When you tell me a bit more about your hot water system I can help with diagnostic suggestions. But without the fuel and type of heater we're shooting too wildly to be useful.

On 2013-03-13 by Kiy

Hot water is not coming through with pressure or heat but cold water working fine.

Boiler seems to be working correctly after checked flow through other outlet so it seems the problem might be in the way the water is feeding back in the house. How can we check where the problem is and what might it be?

On 2012-05-12 by Anonymous

The carpet is wet--dis colored and warm
Could the return water pipe be leaking from the baseboard heater?

On 2012-04-27 - by (mod) -

SMS, some header tubes can be welded, particularly if it's really a crack and without signficant rust damage;

There are also expoxy repair compounds for boilers, though I have not had much success with them. More often the header is replaced.

Mike: putting too much water into a steam boiler can send it up into the steam piping, blocking the movement of steam, leading to cold radiators. If you didn't over-do it, the normal water consumption would have brought the level back down in a few days.

Jim Miller:

Sounds as if there were additives in your heating system, perhaps antifreeze. The leaky pipe needs to be replaced.

On 2012-01-19 by SMS

How to rectify the boiler header tube crack

On 2012-01-16 by Mike

Bryant model 234-55... Have to just water in everyday...before was about every 3-4 days. So I filled with water and went past the glass tube, to see what would happen..well water runs out of the boiler somewhere but cannot see from where.

On 2011-10-23 by Jim Miller

I live in a apartment and the heating pipe is leaking a GREEN LIQUID - What is it and how may it be fixed? - Should I worry? - It has already ruined my Color Printer


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