Blockage !full! — Microbore Central Heating

To understand the blockage, one must first understand the medium. Central heating water is not inert; it is a reactive chemical soup. Over time, the interaction between ferrous radiators (steel or cast iron) and copper pipework creates a galvanic cell, leading to corrosion. The byproduct of this corrosion is magnetite (Fe₃O₄), a black, sludgy substance. In a standard 22mm system, this sludge often settles in the lower loops of radiators, causing cold spots but rarely stopping flow entirely. In a microbore system, however, the pipe’s internal diameter is often a mere 6mm to 8mm. A 1mm build-up of magnetite reduces the cross-sectional area by over 40%. A 2mm build-up constitutes a complete occlusion.

Furthermore, the blockage is rarely pure sludge. It is a composite material: magnetite particles bind with limescale (calcium carbonate) in hard water areas and with flux residues left over from the original installation. When a system is repeatedly turned on and off, the sludge undergoes thermal cycling, hardening into a cement-like substance known as “copper carbonate” or simply “hard sludge.” This metamorphosis transforms a removable deposit into a near-permanent obstruction that can withstand pressures of up to 3 bar. microbore central heating blockage

The ultimate failure of microbore systems is that they were designed without adequate filtration. A modern standard system mandates a magnetic filter (e.g., MagnaClean or Fernox TF1) to continuously remove magnetite. Retrofitting a magnetic filter on the return pipe to the boiler can dramatically extend the life of a microbore system, but it cannot reverse existing hard blockages. Furthermore, the use of corrosion inhibitor (e.g., Sentinel X100) at installation is non-negotiable; an uninhibited microbore system will typically fail within 5–7 years, whereas a treated system may survive 15–20 years. To understand the blockage, one must first understand