Small-diameter copper or plastic tubing, typically 8mm or 10mm, used in central heating systems. Because it is flexible and narrow, it is easy to route through tight spaces, joists, and solid floors. It is often used to connect individual radiators to a central manifold. However, the small internal diameter restricts flow and makes the system highly susceptible to blockages from sludge and scale.
Heard on the job
We've to power flush the whole ground floor because the microbore runs to the hallway rads are completely sludged up.
Insider tip
Microbore systems require clean water and high-quality corrosion inhibitors, as even a small amount of magnetite sludge will choke the flow entirely.