Returned to site to install new Oil Fill Alarm. Disconnected piping to the original Fill Alarm Whistle. New Fill Whistle was a combination Whistle with a Tank Gauge. Moved to the connection on the tank where the original tank was located and plugged the old Whistle connection. Repiped the section of the Fill pipe and added a Union fitting. Once we had the fill pipe apart found the whistle was completely clogged which caused it to fail. Also found that it was not 1-1/4” pipe but was 1” pipe. Let the homeowner know that in the future it may need to be replaced with a larger fill pipe.