Fan of radiator starts when ignition key is on. Earlier itused to start when engine gets heated. This problem has been started after I given my car to change head gaskit and also clean up of radiator for Any jam. But after changing gaskit Also thé car was heating then mechanic changed some oil chamber connecting bearing. Heating problem has been solved but fan problem has been started.
You might try replacing the te, perature sensor. There are two of them, if you have a temperature gauge. If you do then there will be one with one wire which is for the gauge and one with two wires which is for the sensor. Replace the one with two wires. They should be located near the thermostat.