In many UK homes, this is caused by declining system efficiency rather than increased demand. Radiators that once heated evenly may now struggle to distribute heat, forcing the boiler to compensate by running longer.
Sludge and internal restriction are common contributors. Even partial build-up slows circulation, which means heat takes longer to reach rooms. This overlaps with issues covered in radiators that only warm partially and uneven radiator heating.
Heat loss also increases over time as seals degrade and insulation settles. A home that once held warmth well may now lose it faster, increasing boiler run time without improving comfort. The diagnostic tool helps pinpoint where this shift has occurred.
Longer boiler run times paired with lower comfort almost always indicate a system or building issue rather than a failing boiler. The broader explanation is covered in the pillar guide.