This situation often feels confusing because the boiler appears to be doing its job. Radiators may feel warm, the system stays on, and nothing is obviously switching off early. But if heat is escaping through walls, floors, draughts, or poorly insulated spaces, the boiler ends up chasing a moving target. The house warms slightly, then stalls.
Another common factor is distribution. Even when a boiler runs continuously, heat may not be reaching the rooms that need it most. Systems that are unbalanced or have restricted flow can leave some radiators doing most of the work while others barely contribute. Over time, this gives the impression that the boiler is underperforming.
In homes where the boiler runs constantly without achieving comfort, it’s also worth checking whether the system ever truly settles. If the boiler keeps working but the warmth never builds, this is different from systems that stop early or switch off unexpectedly, which is covered separately in boiler turning off before the house warms up.
Long run times can also hide circulation issues. If heat takes too long to move through the system, the boiler stays on longer than necessary without improving comfort. A related pattern where the boiler fires but heat delivery feels weak is explained in boiler fires then switches off, which helps distinguish control issues from heat-loss problems.
When the boiler keeps running but comfort never arrives, stepping back and assessing the whole home usually gives better answers than focusing on the boiler alone. The diagnostic flow here helps narrow down where heat is being lost or misdirected: House Cold Diagnostic.
For a broader understanding of how heat loss, radiator behaviour, and boiler output interact across UK homes, the main guide ties everything together clearly: How to Keep a UK Home Warm for Cheap.