This is the single biggest issue. Because the pipes are so narrow (often just 6mm or 8mm), the system has a very low tolerance for internal debris.
| Scenario | Recommendation | | :--- | :--- | | | Try a chemical cleaner (e.g., Sentinel X400) for 4 weeks, then drain. If that fails, replace that single pipe run. | | Multiple cold radiators | Do not pay for a powerflush (£500–£800). It rarely works on microbore. Replace the manifold and pipe runs with 15mm plastic or copper. | | Plastic microbore | Replace immediately. It is a ticking time bomb. | | System works fine | Add a magnetic filter (e.g., MagnaClean) and use inhibitor annually. Never let the boiler pressure drop to zero. | problems with microbore central heating
Microbore systems rely on a central manifold (a junction block). If a blockage occurs inside the manifold itself, it can knock out an entire section of the house's heating. Locating the manifold can be difficult, as previous homeowners may have buried it under flooring or boxed it in. This is the single biggest issue