I think the letter I in your model number is a number 1. Have you checked the White Rodgers website at the link shown here, they should have all the manuals for their 80 Series here...
http://www.white-rodgers.com/wrdhom/common/ptech/thermo/info_list_ss.htm#1F80-224
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Looks like someone else found a link specifically for the 1F80-261 in a different thread, so I'll repost it here for you...
http://www.arpis.com/residential/docs/1F80.pdf
White Rodgers Thermostat 1F80-51 troubleshooting 1f80-51 I changed batteries and now the display is flashing with all characters fo the display on. For exam…