This situation often appears when hot water is being produced but not distributed effectively. The boiler is doing its job, but the heat isn’t reaching the rooms in a useful way. Poor flow through the system is a common reason, especially in homes where radiators closer to the boiler warm slightly while others remain cool.
Balancing plays a major role here. If certain radiators are taking most of the flow, the rest of the system is left underfed. This can make it seem like the boiler is running for no reason. Correcting this usually restores proper heat delivery, which is why balancing is covered in detail in this radiator balancing guide.
Another factor is internal air or partial blockages. Radiators that look fine on the surface can still restrict circulation internally, slowing heat transfer across the system. This often overlaps with problems where radiators take a long time to respond, as explained in why radiators take so long to heat up.
If the boiler is clearly running but the house remains cold, working through the system logically is far more effective than adjusting boiler settings at random. The house cold diagnostic helps separate boiler behaviour from circulation and heat-loss problems.
For a full explanation of how these issues connect in real UK homes, the reference point is the main guide on keeping a UK home warm for cheap.