Leaky steam radiator (C) Daniel Friedman Q&A on Leaky Radiators, Baseboards, Convectors
FAQs on how to fix leaky baseboards / radiators

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Heating radiator leak troubleshooting FAQs:

Questions & answers on how to find and fix leaky radiators or baseboards.

This article series describes how to find and fix leaks in hot water heating radiators. We describe the types and locations of leaks found on heating radiators: hot water, steam, cast iron, heat convectors, basn radiators, between abutting radiator sections near the bottom of the unit.

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FAQs on How to Fix Leaks on Baseboards, Radiators, or Heat Convectors

Heating baseboard leak (C) Daniel Friedman

These questions & answers about diagnosing & fixing leaks in heating baseboards, convectors, or hot water or steam radiators were posted originally at LEAKS at BASEBOARD, CONVECTOR, RADIATOR

On 2017-08-25 by (mod) - what sealant to use when connecting leaky radiator sections


Thanks for a great radiator leak repair question. Indeed millions of cast iron radiators are made of sections squeezed together with push-nipple connections that do not use a gasket, relying on clean-surfaced, properly-shaped mating metal surfaces.

I think your idea of an epoxy repair is reasonable but maybe not the best in that a future repair at the same radiator could be rendered more difficult by the epoxy.

If the surfaces are not very badly corroded I'd clean them and then see what non-epoxy sealant your plumbing supplier recommends that will seal the joint tightly but will permit future disassembly - such as a high-temperature-tolerant silicone seal used on automotive engines.

On 2017-08-25 by Charlie

I have low profile cast iron hot water radiators. They are assembled in sections. I have a leak between 2 sections. The joiners are short tubes aprox. 3" long. Not threaded. The sections are pulled together by a 1/2" thread size carriage bolt. The old bolt was rotten when I disassembled the leaking section. Is this just a machine fit held together by the bolt? If that is so can I use a sealer or epoxy on the connection when I re-assemble?

On 2017-01-10 by (mod) - using radiator sto leak products - warning

Anon: yes there are stop-leak products for boilers that might seal an under-floor piping leak.

Watch out: However some technicians worry (and I agree) that such products might clog something that they shouldn't, thus making the system unsafe. For example I don't want to use a stop-leak product that clogs a dripping relief valve or we might end with a BLEVE EXPLOSION (search InspectApedia for that term).

You should certainly not have to rip out the floor. Just abandon that in-floor piping loop by sealing the heating system pipes that enter it and leave it.

On 2017-01-09 by Anonymous

I live in a house where there are heating pipes that run through the concrete basement floor.

We don't turn that section of the heating system on any longer, we think there's a leak. Is there anything on the market that we could pour in the tank and have it circulate through the system and seal the leak? Let's face it, we don't have the money to rip out the floor and replace it

On 2016-12-04 by David

I have a cast iron radiator it's leaking at the bottom of right hand side can it be fix if is at the joint

On 2016-11-26 by (mod) - pattern of corrosion development in hot water heating systems


It's reasonable that in an older heating system whose heating water was corrosive, several points of corrosion may be developing at once. In addition to checking the chemistry of the boiler water, you'll want to have your expert check that the system was operating at a normal pressure range. Else the system is unsafe.

On 2016-11-26 by Autumn

I just had two baseboard cast iron radiators blow out in two different rooms in two days time... One each day.

We used the boiler last year with no issues and it's not cold enough to have frozen this year. It had been running for about 3 weeks with no issues. Flooded our office and ruined the carpet. We now have it completely shut off. Anyone know what may be causing this?

On 2016-11-13 by (mod) - can I fix a leaky radiator myself?


First you want to know where the leak is. A leaky plumbing connection (say at a threaded fitting or a radiator valve) can be repaired, probably by a plumber or a very handy homeowner. But a leak showing that a radiator is rusting-through is much more difficult. The cast iron will have a larger thinned fragile area than just the point where you see water dribbling out.

You might make a *temorary* repair by shutting off the heat, letting the radiator cool, cleaning the leak area carefully down to bare metal, then applying a plumber's epoxy intended to seal leaky cast iron or other piping. But I'd be left nervous about a leak recurring when nobody's home.

On 2016-11-13 by Cathy

I have a leaking cast iron radiator In a 100+ year old house. Is this something I can repair myself. If yes how?

On 2016-11-08 by (mod) - how to prevent baseboard leaks and water damage


Great question and a difficult one. You can inspect for signs of rust and rust perforation, but the limitation is that much of the baseboard heater and its piping will not be visible.
I'd want to know more about the leaks that occurred.

Did the leak occur at a badly-made plumbing connection, at a point of corrosion, or due to an excessive pressure condition in the heating system?
In a commercial building it may be useful to have an expert test the boiler water for corrosivity and thus to decide if treatment is needed.

On 2016-11-07 by David

Hi there I live in a building with hot water baseboard heating. Last year two units in my building had major leaks where the pipe in the floor hot water baseboard heater burst causing flooding to the whole unit and surrounding units. At the time it happened neither of the tenants were home.

As a result I've been very anxious that the same could occur in my unit.
Is there any way that the baseboard heaters can be inspected to prevent this from happening?

On 2016-06-21 by (mod) - how to send photos to InspectApedia for posting or comment

Use the page top or bottom CONTACT link to send us photos for comment.

On 2016-06-20 by Anonymous

Thankyou for your reply danjoefrieman. It's a modern radiator - is there any way I can post a photo to show you? I take on board what you've said though. Many thanks.

On 2016-06-19 y (mod) - cast iron radiator leaks can be repaired or not?

Madee, I'm guessing this is a cast iron radiator leaking between sections. Your heating service tech might want to try adding a stop-leak product to the system for a band-aid type repair but I don't like that approach as the goop can clog other system components and prevent their proper, safe operation;

You can also try an external expoxy repair to defer replacing the radiator.

On 2016-06-19 by Madee

A bubble has appeared near the top of a radiator installed about 15 years ago.There is now a rust stain running down the radiator. When the radiator is cold, we have to catch the drips that run down from the bubble with newspaper. Can it be repaired or do we need to buy a new radiator. Thankyou.

Question: bath tile damage due to steam heat moisture

(Feb 9, 2015) Anonymous said:
I have steam heat and in the bathroom the floor tiles are coming up due to the moisture. Granted, I haven't replaced the floor since I bought the home in 1991. When I do replace the tiles, would it be smarter to get ceramic floor tiles instead?



The ceramic tiles are more water resistant, won't address hidden damage to the subfloor, and might cause trouble if you have to raise the radiator to get it up onto the thicker tiles.

Question: radiator leaks keep getting worse

(July 18, 2015) Gerry said:

I have a 63 year old 2 story cape cod house in coastal Virginia with hot water hydronic heat provided by an oil fired boiler. This boiler also provide domestic hot water, and all 3 zones of heat. Pipes in the crawl space are leaking right at a series of mono-valves?

It started as one leak, and after a season of it leaking and refilling without my knowledge, the situation has apparently gotten worse? Can I recover and just repair a series of these valves or should I consider the longer term and abandon the hydronics? This is currently a 3 zone AC setup. Zone 1 is 1.5 ton, 3 bedrooms up and 2 bath's up on a new heat pump which has not ever been used for heat.

2nd zone is a small 'Apollo' unit, AC only, outside compressor and hot water from the boiler uses a coil in the air handler to heat our converted garage, i.e. 1 upstairs bedroom and a downstairs living space. The balance one of the downstairs is AC'd off a single 2 ton self contained 'gas pack' unit that could be swapped out for a "gas pack" heat pump I suppose.

Then I'd be faced with pulling out 15 recessed radiators and patching old walls, some plaster, some tile, some paneling. Its a tough decision, I believe the fresh rust was because of excess oxygen getting in the system this past winter due to a leak gone undetected. Any feedback would be greatly appreciated.


I'd get an estimate on cutting out and replacing the leaky valves; it'd be odd for the whole piping system and radiator set to be replaced unless there have been other unattended leaks or unusually corrosive conditions in the boiler water.

Question: rust smell from radiator

(Mar 14, 2016) Aida said:
I live in a privately owned co-op---When radiator is on---the smell of rust comes up with the heat--should I be concern about this ?

As I mentioned earlier---The privately owned co-op is old (late 1940's)--I doubt it very much if there has been any upgrade-

-I've lived here 14 years--but, the rusty smell from my radiator began in Oct./2015---I have reported the problem---they indicated that there was a crack in one of the pipes inside wall--the maintenance supervisor has refused to repair the pipe---I can't continue to breath-in this rusty smell--I need to know if my health is in jeopardy


From just your text, Aida, I'm not sure what's going on and can't assess possible hazards that may be involved. Certainly if building materials such as wood, drywall, insulation, carpets - are being wet, there may be a mold growth hazard.

I'm not sure what the rusty smell is - perhaps it's smelly water or gases from a hot water heating system (i.e. not steam).

Certainly water in hot water heating system piping and radiators is often stinky as the same water, sometimes plus boiler chemicals and possibly with some hot-water tolerant bacteria can remain for a long time.

But no one being honest with you would pretend they could evaluate the health risk to which you're exposed simply from a message.

First let's get leaks fixed and any spills cleaned-up.

Question: leaky neighbour's radiator ruined my ceiling. Was I exposed to asbestos?

(Apr 1, 2016) Anonymous said:
Hello, my upstairs neighbors' radiator was leaking for a few months and it ruined a part of my ceiling.

Maintenance fixed it recently: first, they they removed damaged part of the ceiling (up to the point where I could see metal structure) and put trash in a grocery brown bag and left it in my apartment for a few days, while he ceiling hole was drying. Then they fixed the ceiling. The building is near 100 years old, it is 20-story building.

Is there a possibility I was exposed to asbestos anytime during the process? As in, was asbestos used for insulation predominantly in basement (which this building hadand they removed it few weeks ago) or was was also used for insulation anywhere near radiators, in-between floors? Thank you.


Anon: naturally no one can assert for sure what exposures might have been present from an e-text about an unknown building , but I can note that if the dust was controlled and properly cleaned-up after the work (HEPA vacuuming, damp wiping), the exposure remaining would be expected to be very low.

If it's worth $50. to you to lower your worry, you could collect a representative sample of settled dust (clear adhesive tape, plastic bag) and send that to an asbestos test lab. If you do so, keep me posted - what you find may help others.


Question: drips from the radiator

2016/06/19 Madee said:
A bubble has appeared near the top of a radiator installed about 15 years ago.There is now a rust stain running down the radiator.

When the radiator is cold, we have to catch the drips that run down from the bubble with newspaper. Can it be repaired or do we need to buy a new radiator. Thankyou.


Madee, I'm guessing this is a cast iron radiator leaking between sections. Your heating service tech might want to try adding a stop-leak product to the system for a band-aid type repair but I don't like that approach as the goop can clog other system components and prevent their proper, safe operation;

You can also try an external expoxy repair to defer replacing the radiator.

Later discussion and photos led us to make the suggestions now found at LEAKS in STEEL RADIATORS

Question: leaks in heating boiler after shaking, rattling, and steam came out of floorboards

(Nov 17, 2014) joints in central heating leaking said:

Hi, we just put on the heating after summer. It seemed ok, but then the boiler started shaking and rattling and there was steam coming through the floorboards. It continued a bit after shutting off the boiler (gas, 24 y old).

Then, we found a leak in a metal T-joint leading off to radiators (near boiler). We have a mixture of metal and plastic piping. The joints are all metal of course. The leak was caused by the plastic pipe coming out of the joint. We replaced the joint. Refilled system with water.

Seemed OK, but this time a leak sprunt in the bathroom (2 floors up), again, plastic pipe into metal joint. We tightened a nut that seemed loose and it hasen't leaked since. We put on the heating with just that one bathroom radiator on to test it, but the boiler got very hot, the thermostat didnt seem to cut off. We switched everything off again.

We let it cool. The boiler man (on phone) said that just having one radiator on could have caused that problem, especially as the expansion tank is needing replacing (which will be done soon).

He said that if we switchen on more radiators everything should be ok.

We put on the heating, switched on extra radiators, everything seemed OK, but now two new leaks have just appeared: one in the pipe going into the radiator (rad was off at the time of leak) (again plastic pipe into a metal joint). The other leak is hidden behind boarding (that I am ripping down now) but it seems to on upright pipes on the 1st floor that bring heated water to radiators directly from boiler.

This is a 100 year old+ house, and we had some new rads installed 10 years ago on a tight budget.

I would appreciate if someone could explain a likely reason why the leaks are happening. Bad workmanship ? Too high pressure in system? Water too hot in system? The expansion tank ?

Thanks in advance for any comments at all.

I forgot to say that before the boiler got very hot and the thermostat didnt cut off, I had set it to 90 degrees celsius instead of the usual 60 degrees celsius.

which was a dumb thing, and we set it back afterwards.

me again, just to say that all the leaks are in separate places and on different joints. Basement = 1 leak, 1st floor= 1 leak, 2nd floor = 3 leaks (1 x hallway rad, 1 x near bathroom rad, 1 x big pipes that bring water to top of house (3rd floor)).



Really? I can't imagine what a heating tech is thinking in saying it's ok to have steam coming up through a floor.

Leaks in stem piping are not fixed by turning on more radiators. It sounds as if you need help from a plumbing and heating contractor who is familiar with steam piping and controls.

Question: mold growth due to steam vent leaks

9 Jan 2015 Maria said:
I have a radiator that blows out vapor steam. So much that mold is growing on the wall and there are what looks like balls of jell on the ceiling as well. Is this harmful.



One can't assess the harmfulness of mold by just a brief e-text but usually a large indoor mold reservoir that has grown on surfaces is at least allergenic and possibly pathogenic or toxic - depending on the genera/species and further depending on what the mold is growing-on. Large areas, more than 30 sqft. deserve professional cleaning.

You should repair or replace the steam vent that I infer from your note is failing to close when it should. I suggest that you continue reading at STEAM RADIATOR VENT REPAIR

Question: ammonia odor and possible radiator leaks?

(Feb 27, 2012) Thank you said:
There has been a sharp ammonia like odor in my apartment stinging my eyes, nose , throat and hurting my lungs.

I have been cleaning and ventilating for days even though its only 30 degrees outside. I've been searching with frustration of people who don't pay attention saying it's urine when I know it is not.

Thank you for an intelligent and more accurate answer. Now we can work on finding a solution that works. Any suggestions until the landlord gets here to fix it? How do I get it out of the warped wood floor?


At ODORS GASES SMELLS, DIAGNOSIS & CURE - we give diagnostic suggestions for tracking down and fixing any odor including ammonia smells. Often indeed those are found to originate in urine but there could be other sources. First find the physical source

It would be unusual for ammonia smells to come from a leaky radiator but heating a radiator may cause it to emit odors from something that was painted on or spilled onto that device.



Continue reading at LEAKS at BASEBOARD, CONVECTOR, RADIATOR or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see STEAM RADIATOR VENT REPAIR if your radiator leaks are at a steam radiator vent

Or see CHEMICAL TREATMENTS, BOILER for a discussion of leak-stop products used in heating systems

Suggested citation for this web page

BASEBOARD or RADIATOR LEAK REPAIR FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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