Pixma TR8520 - Fax picking up even though it set to have the Telephone as priority

[rice-shop]

I just setup my multifunction printer yesterday.  I since I use one phone line for telephone and faxing I set the machine to have the Telephone as priority.  Last night we got a call in, and about 30 seconds after I answered the phone, the fax kicked in and started it's thing.  The only thing I could do was to shut off the printer.  I went back through the settings this morning and the only option I can find is to set the Telephone as priority.  Is there a way to set it so that Fax can be initiated manually?

[Patrick]

Hi rice-shop,

Is the phone that you are answering the incoming call with connected to the EXT jack on the back of your PIXMA TR8520?

[rice-shop]

No the FAX is plugged into a wall jack that shares the same phone line as the phone.