When a hot water radiator reaches 43 degrees or more, it can cause instant scalding or burns to any person who comes into contact with it. A risk of serious injury is posed, so radiators should never be allowed to reach such a temperature.
Generally speaking, it is recommended that home radiators work somewhere between 18 and 22 degrees to provide a comfortably warm ambient temperature in a home.
For further information, consult our blog, Are your radiators too hot?