Aprilaire 8551 - Manual (Page 17)

No. 2 – Keypad Lock. If tampering with the thermostat is expected and unwanted, the keypad can
be locked by moving this switch from the factory set OFF position to the ON position. This should
not be done until all programming is finalized. In the locked position only the following functions
can be done:
• The outdoor temperature button will display the outdoor temperature.
• The DECREASE button or INCREASE button will temporarily change the
set point a maximum of plus or minus 3 degrees for a period of 1 hour, before the
thermostat automatically returns to the original program.
If the thermostat does not respond when a button is pushed it may be because the keypad has
been locked. A Lock icon “ “ will appear when pushing any buttons other than the buttons
outlined above.
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