Boiler corrosion is a major problem that can shorten the life of your heating system and require expensive repairs or replacement. Knowing the causes and prevention techniques is important for ensuring your boiler's efficiency and lifetime.

Causes of Boiler Corrosion

Dissolved Oxygen

Dissolved oxygen is a primary culprit in boiler corrosion. When oxygen reacts with metal components, it forms iron oxide, leading to material degradation. This process occurs in feedwater, boiler water, and condensate systems. Even small amounts of dissolved oxygen can cause significant damage over time, making its removal crucial for boiler longevity.

Dissolved Gases

Carbon dioxide and hydrogen sulphide are particularly problematic dissolved gases. These gases create acidic conditions within the boiler system, accelerating corrosion. Carbon dioxide forms carbonic acid, which lowers pH levels and attacks metal surfaces. Hydrogen sulphide is equally corrosive, reacting with metal to form metal sulphides.

pH Levels

Maintaining proper pH balance is essential for preventing boiler corrosion. Low pH levels increase acidity, leading to accelerated metal dissolution. Conversely, excessively high pH can cause caustic corrosion. The ideal pH range for most boiler systems is between 8.5 and 9.5, depending on the specific boiler design and operating conditions.

Deposition

Iron deposition and scale buildup contribute to under-deposit corrosion. These deposits create localised areas where corrosive substances can concentrate, leading to accelerated metal loss. Scale formation also reduces heat transfer efficiency, potentially causing overheating and thermal stress corrosion.

Water Quality Issues

Poor water quality is a primary cause of boiler corrosion. High mineral content in hard water areas can lead to scale formation, while incorrect pH levels can accelerate metal deterioration. Dissolved oxygen in the system water continuously attacks metal surfaces, and any chemical contamination can create aggressive corrosive conditions. Regular water quality testing and appropriate treatment are essential for preventing these issues.

System Design Problems

Poor system design can create conditions that promote corrosion. Inadequate water treatment facilities, poor circulation patterns, and dead legs in pipework all contribute to corrosion risk. Incorrect venting can trap air in the system, leading to oxidation and subsequent corrosion. A well-designed system should incorporate proper circulation paths, adequate venting, and appropriate materials selection.

Maintenance Neglect

Regular maintenance is crucial for preventing corrosion. Delayed repairs of minor leaks can lead to more significant problems, as can failure to check water quality regularly. Ignored warning signs often result in accelerated deterioration, while skipped annual servicing means potential issues go undetected until they become serious problems.

Types of Boiler Corrosion

Oxygen Corrosion

Oxygen corrosion occurs when dissolved oxygen in the water reacts with metal surfaces. This creates rust and pitting, which can eventually lead to system failure. You might notice rusty water coming from your taps, pinhole leaks developing in pipework, red or brown deposits forming around joints, and a noticeable reduction in heating efficiency. These signs indicate that oxygen is actively corroding your system.

Scale Formation

Scale forms when minerals in hard water build up inside the boiler. This not only reduces efficiency but can also lead to localised corrosion underneath the scale deposits. The impact of scale formation manifests through reduced heat transfer, increasing energy bills, unusual noises from the boiler, and uneven heating throughout your home. As scale builds up, it creates a barrier between the heat exchanger and the water, forcing your boiler to work harder to achieve the same temperature.

Galvanic Corrosion

This occurs when different metals in the system come into contact, creating an electrochemical reaction. Modern boilers are designed to minimise this risk, but it can still occur in older systems or poor installations. When galvanic corrosion takes place, it typically affects the joints and connections where different metals meet, leading to weakening and eventual failure of these crucial components.

Get professional advice from heating engineers in Telford, Newport and Shrewsbury

For expert advice on preventing boiler corrosion or addressing existing issues in Telford, Shrewsbury, Shifnal, or Newport, contact our team of gas engineers at 01952300008. Our Gas Safe registered engineers provide comprehensive system assessments, recommend appropriate preventive measures, perform necessary maintenance, and can install corrosion prevention equipment when needed.