This behaviour is common in radiators positioned close to the boiler or on shorter pipe runs. Hot water reaches them first and at higher pressure, so they warm rapidly. As the rest of the system catches up, flow evens out and that radiator often loses its advantage, cooling sooner than others.
The most frequent cause is imbalance. Radiators that are overfed early on effectively starve slower radiators elsewhere in the house. Once the thermostat or TRV reacts, the flow changes and the fast radiator stops receiving heat. This pattern is closely linked to wider balancing issues, which are explained in detail here: How to Balance Radiators Properly.
Valve behaviour can also influence this. A wide-open lockshield or a TRV reacting quickly to room temperature can cause the radiator to shut down earlier than expected. The radiator itself isn’t faulty — it’s responding to how the system is prioritising flow.
This effect sometimes overlaps with cases where radiators heat unevenly across the house, especially between floors. If you’ve noticed similar behaviour elsewhere, this article provides useful context: Radiators Heat Unevenly Across the House.
If you’re unsure whether the issue is isolated or part of a broader system pattern, the diagnostic page helps identify where the imbalance is likely occurring: House Cold Diagnostic.
Correcting this kind of imbalance usually results in all radiators heating and cooling more consistently together. That not only improves comfort but also helps the heating system run more efficiently overall, which is covered in the wider context of keeping heating costs down here: How to Keep a UK Home Warm for Cheap (Complete Guide).
