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What Causes Sediment Deposits on Copper Pipes in a Central Heating System?

matgor23 15702 20
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  • #1 17639348
    matgor23
    Level 10  
    Hello

    I have deposits on the pipes as in the attached photo, tell me what this may be caused by? It was created some time after the boiler was in operation. Is it normal? What Causes Sediment Deposits on Copper Pipes in a Central Heating System? What Causes Sediment Deposits on Copper Pipes in a Central Heating System?
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  • #2 17639399
    viayner
    Level 43  
    Hello,
    There may be several sources, for example:
    - water codensation, in a slightly alkaline/acidic environment and you have corrosion products
    - leaks of water containing a lot of carbonates (hard water), evaporation of water and crystallization of carbonates.
    - if you have contact of different metals, you have "electrochemical" products, a cell is created.
    Regards
  • #3 17639404
    matgor23
    Level 10  
    Could this cause air to appear in the installation?
  • #4 17639426
    viayner
    Level 43  
    Hello,
    it looks like surface deposits, I don`t know what your environment is? brazed pipes - how are they connected? Warm water accelerates corrosion processes, although copper is a metal on the "precious" side, corrosion occurs, it`s all a matter of conditions.
    Can you determine the source of the problem? leak, thin stream or rather condensation?
    Regards
  • #5 17640288
    matgor23
    Level 10  
    There are no leaks. The environment is as in the second photo, i.e. just an ordinary home boiler room, about 6 m2
  • #6 17640317
    slider2002
    Level 15  
    In my opinion this is the norm. copper reacts vigorously. these deposits should be easy to remove.
  • #7 17640358
    Anonymous
    Anonymous  
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  • #8 17640495
    Plumpi
    Heating systems specialist  
    Such deposits are the result of the sloppiness of the installer who did not want to clean the tubes after soldering to remove any solder paste remnants. Solder paste contains acids and powdered tin.
  • #9 17643253
    VPS
    Level 25  
    That`s why it`s always worth having a damp microfiber and ALWAYS wipe the place after soldering. You can then paint with copper spray.
    Buy yourself a copper pipe cleaner and clean these places.
    What Causes Sediment Deposits on Copper Pipes in a Central Heating System?
  • #10 17643487
    Zbigniew Rusek
    Level 38  
    viayner wrote:
    Hello,
    it looks like surface deposits, I don`t know what your environment is? brazed pipes - how are they connected? Warm water accelerates corrosion processes, although copper is a metal on the "precious" side, corrosion does occur, it`s all a matter of conditions.
    Yes, copper is rather resistant to corrosion, but slightly less than brass (an alloy of copper and zinc), in which the addition of zinc increases the resistance to oxidation.
  • #11 18990094
    zwiezda
    Level 9  
    What is this coating on the copper pipe supplying gas to the stove? what to wash it off and preserve it with? What Causes Sediment Deposits on Copper Pipes in a Central Heating System?
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  • #12 18990787
    viayner
    Level 43  
    Hello,
    Copper is subject to corrosion, depending on the environment, it may be oxides or sulphides (these are the most common), the greener ones are basic carbonates - malachites - see church roofs.
    These are surface raids.
    Regards
  • #13 18990796
    bratHanki
    Level 39  
    The installation was made with brazed copper solder with an admixture of several percent phosphorus, so this coating may be some of its salts.
  • #14 19463612
    olekolo
    Level 10  
    And today, using an inspection camera behind the bathtub, I saw something blue on the radiator pipe. It looks like a piece of mortar that has turned blue, is this normal?
    Attachments:
    • What Causes Sediment Deposits on Copper Pipes in a Central Heating System? Screenshot_2021-06-03-09-43-14-718_com.tony.usbcamera.molink.jpg (967.1 KB) You must be logged in to download this attachment.
  • #15 19463743
    viayner
    Level 43  
    Hello,
    this is malachite, a basic copper carbonate, formed as a result of the corrosion of copper in an alkaline environment, a completely normal and surface phenomenon, compare, for example, the roofs of churches covered with copper. The color may be between green and blue, depending on corrosion conditions
    Regards
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  • #16 19463771
    olekolo
    Level 10  
    Thank you for your answer. So it won't eat through my knee :)
    I know that a greenish coating is normal. I was surprised by the blue one. The backlight may be a bit misleading, but the blue one surprised me. And I'm a bit oversensitive because in my previous apartment everything was made of indestructible copper and it washed out my elbow
  • #17 19463817
    viayner
    Level 43  
    Hello,
    it all depends on whether the "environment" in which this element works is acidic or alkaline, more or less humid, etc. it is still the same substance but with a slightly different relative composition.
    Regards
  • #18 19463820
    olekolo
    Level 10  
    Cool. I see. And one more question. Because I understand that the pipe itself is covered with malachite. But it looks like it would be thicker. If the mortar from the tiles fell and it was covered with malachite, there is no possibility that the tile or plaster glue would react in such a way that it would eat away at the elbow?
  • #19 19464349
    viayner
    Level 43  
    Hello.
    Since you mention that you may have, for example, plaster on a copper pipe and the whole thing is in a corrosive and humid environment, you probably have a layer of plaster saturated with copper ions and they react to form the above-mentioned malachite on the copper surface.
    Note that if the entire pipe is in a corrosive environment and, for example, immersed in water, all the water will be susceptible to the formation of malachite, and it will form where it is easiest to initiate crystallization, i.e. porous places.
    Copper corrosion is rather superficial, what may be dangerous is the formation of an electrochemical cell, i.e. contact of two metals (different, with different potentials) and the contact is ensured by an electrolyte (water with some salt). In this case, the more active, less noble metal will be damaged.
    Regards.
  • #20 19464448
    olekolo
    Level 10  
    I see. Thank you for your answer, I will sleep more soundly. It`s all in copper there. The tubes are in the air. They don`t touch anything. Thanks and it`s no longer poisonous.
  • #21 19603201
    Michaljaros1
    Level 4  
    Hello.

    I will join the thread with my problem.
    Basically, after reading this, I know more or less what and how.
    I have a copper gas installation in the hen houses. Chicken manure itself contains a lot of nitrogen and ammonia.
    In addition, when cleaning, I use ammonia, sodium hypochlorite, lime and many other substances.
    Is it possible to check whether it is a surface sediment or whether it has gone deeper?
    The closer to the ridge, the worse, but that`s where the moisture comes in.
    In the worst places it fades to black.

    Regards

    What Causes Sediment Deposits on Copper Pipes in a Central Heating System? What Causes Sediment Deposits on Copper Pipes in a Central Heating System? What Causes Sediment Deposits on Copper Pipes in a Central Heating System?
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Topic summary

✨ The discussion revolves around the causes of sediment deposits on copper pipes in a central heating system. Various contributors suggest that these deposits may arise from several factors, including water condensation in an alkaline or acidic environment leading to corrosion, the presence of hard water causing carbonate crystallization, and residues from soldering flux. It is noted that copper, while generally resistant to corrosion, can still develop surface deposits due to environmental conditions. The deposits are often considered normal and can be easily removed. Concerns about air in the system and the potential for electrochemical reactions due to contact with different metals are also raised. The discussion emphasizes the importance of proper installation practices, such as cleaning soldered joints to prevent residue accumulation.

FAQ

TL;DR: Most copper‑pipe deposits come from 3 causes—condensation corrosion, hard‑water leaks, or galvanic contact; "a cell is created." Identify the source, then remove surface deposits and reduce moisture or metal contact. [Elektroda, viayner, post #17639399]

Why it matters: This FAQ helps homeowners and installers diagnose and clean copper heating or gas lines, preventing repeat build‑up and premature joint failure.

Quick Facts

  • Typical copper patina is malachite (Cu2CO3(OH)2) with green–blue hues; color shifts with environment. [“Malachite”]
  • Standard practice: after soldering, wipe joints with a damp microfiber; optionally coat with copper spray; use a copper pipe cleaner. [Elektroda, VPS, post #17643253]
  • Flux residues contain acids and powdered tin; uncleaned joints develop crusts and staining. [Elektroda, Plumpi, post #17640495]
  • Design rule: avoid dissimilar metal contact in an electrolyte; the less noble metal corrodes faster. [Elektroda, viayner, post #19464349]

What causes green/white deposits on copper pipes after a boiler starts?

Three common sources: condensation creating corrosion products, leaks of hard water leaving carbonate crystals, and electrochemical reactions where dissimilar metals touch. Identify which applies by checking for dampness, crust near joints, or mixed-metal contact points. Then correct the cause and clean the surface. [Elektroda, viayner, post #17639399]

Is seeing deposits on new copper joints normal?

Yes. Fresh copper reacts and light deposits can appear, especially near new soldered joints. "These deposits should be easy to remove." Clean the area and monitor. If deposits return quickly, look for moisture, flux residue, or mixed-metal contact as underlying causes. [Elektroda, slider2002, post #17640317]

Could leftover solder flux be the reason?

Yes. Residual solder paste contains acids and tin powder. If not cleaned after soldering, it can attract moisture and form crusty deposits. Wipe and mechanically clean joints after soldering to remove flux and stop recurrence. Persistent deposits may indicate remaining flux or hidden moisture. [Elektroda, Plumpi, post #17640495]

How do I clean the joints and stop it coming back?

Use this 3‑step method:
  1. Wipe the joint with a damp microfiber immediately after soldering or when deposits appear.
  2. Mechanically clean with a copper pipe cleaner or Scotch‑Brite.
  3. Optionally apply a light coat of copper spray for protection. [Elektroda, VPS, post #17643253]

Will these deposits introduce air into my heating system?

Surface deposits don’t create air. Air usually comes from small leaks, fresh fill water releasing gas, or maintenance. Inspect joints for dampness or condensation tracks and fix those first. Bleed radiators after repairs. If deposits keep forming, recheck for hidden leaks. [Elektroda, viayner, post #17639426]

I see a blue patch on mortar or plaster near a copper pipe—is that normal?

Yes. Alkaline mortar or plaster can trap copper ions and foster malachite on or within porous spots. The result appears green to blue and is typically superficial. It forms where crystallization starts easily, such as on rough, absorbent material touching the pipe. [Elektroda, viayner, post #19464349]

What if the deposit looks black or dark instead of green?

Dark films often indicate copper oxides or sulphides formed under specific environmental conditions. Edge case: in ammonia‑rich, humid buildings, black sulphide films can develop faster. Clean the surface and improve ventilation or humidity control to slow recurrence. [Elektroda, viayner, post #18990787]

Will corrosion eat through my elbow or pipe wall?

Patina on copper is generally a surface phenomenon, not deep pitting. "It is a completely normal and surface phenomenon." Worry more about galvanic pairs plus moisture. If different metals touch and stay wet, the less noble metal can fail. [Elektroda, viayner, post #19463743]

How can I tell condensation from a leak or a galvanic issue?

Condensation leaves widespread moisture during cool‑down and light, uniform films. Leaks leave localized wetness or trails and fresh scale. Galvanic issues cluster around mixed‑metal junctions. Start by checking for leaking drips or a thin stream, or signs of condensation. [Elektroda, viayner, post #17639426]

Should I paint copper joints after cleaning?

It’s optional but useful in humid spaces. After wiping and mechanically cleaning, a light copper spray can add cosmetic protection. Focus first on removing flux and stopping moisture. Paint is not a substitute for fixing leaks or mixed‑metal contact. [Elektroda, VPS, post #17643253]

Is brass more corrosion‑resistant than copper in this context?

Yes. Brass, a copper‑zinc alloy, shows improved resistance to oxidation compared with pure copper. It can reduce visible patina formation. Use appropriate fittings and respect gas/water codes when mixing materials. Always avoid creating galvanic couples with electrolytes present. [Elektroda, Zbigniew Rusek, post #17643487]

Could the coating come from phosphorus in the brazing alloy?

Yes. Many copper brazing solders contain several percent phosphorus. Salts from these alloys can contribute to visible films near heated joints. Clean thoroughly after brazing to remove residues and reduce staining. If films persist, check for moisture or dissimilar metal contact. [Elektroda, bratHanki, post #18990796]

I have copper gas lines in a chicken house—are these films only surface?

In ammonia‑ and nitrogen‑rich air, copper can form oxides or sulphides on the surface. These are typically superficial films. Improve ventilation and dryness to slow formation, and clean surfaces periodically. Inspect joints and supports where moisture can linger. [Elektroda, viayner, post #18990787]

What’s actually dangerous about copper pipe corrosion here?

The bigger risk is galvanic corrosion when different metals touch and an electrolyte is present. Then the less noble metal degrades faster. As one expert puts it, "Copper corrosion is rather superficial"; manage galvanic couples and moisture instead. [Elektroda, viayner, post #19464349]
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