Instead of checking the heat at the top of the radiator, also check what the temperature is like at the base of the radiator also.
This radiator was down 35% in temperature in the lower section.
Over time, sediment builds up in your heating system, settling in the radiators and reduces their efficiency.
So you are still paying£ at the boiler but not benefiting fully from the heat. if this is the case, it’s time to chat to your heating engineer about flushing the radiator or the whole system. This is part of the many checks we do across the house during our Heat Loss Surveys.