I have a White Rodgers 1F90-51 Thermostat. Yesterday an alarm went off that was only stopped by removing the 3 AA batteries. New batteries didn't solve the problem. Is the unit defunct or is there something I'm missing?

Here is your complete owners manual

http://www.white-rodgers.com/wrdhom/pdfs/instruction_sheets/0037_5099_B.pdf

Here is your complete install manual

http://www.white-rodgers.com/wrdhom/pdfs/instruction_sheets/0037-5043rev_B.pdf

The information you are looking for showld be in these manuals

My name is Tim Burke from White-Rodgers. If the thermostat is continually beeping there is no way to repair it. It will need to be replaced. That is a pretty old thermostat. You may want to look at our newest line The Blue series of thermostats. You can see information on them at www.white-rodgers.com If you want to purchase on line you can go to Shop Programmable Thermostats from Honeywell, White-Rodgers, Robertshaw and more (http://www.prothermostats.com)

Best regards