Pilot lite will not stay lit on boiler under tank it lites then goes out when i turn switch to on?

You have a bad thermocouple. The thermocouple is a safety feature that is heated by the pilot flame and it closes the main gas valve if the pilot flame goes out. No gas will flow through the gas valve to the main burner if the thermocouple is bad and the pilot gas line will also shut off when you turn the main burner gas valve to on.