Why HIU strainers block
Communal heating networks carry magnetite, jointing compound, pipe scale and installation debris, and it all ends up at the first fine mesh it meets — the strainer in your HIU. New schemes block quickly during their first year as construction debris circulates. Older schemes generate magnetite continuously from corrosion. Either way the mesh fills, flow drops and the unit slowly stops performing while looking perfectly healthy from the outside.
- Construction debris on new and recently altered schemes
- Magnetite from system corrosion on older networks
- Scale and jointing compound from pipework
- Debris released after network repairs or drain-downs




