My furnace blower motor has been acting up so I ordered a new blower motor. Meantime the furnace decides to stop working and it disappears from the thermostats menu of options! Nothing about that in my manuals and could not find anything about it on the forum, so I called a commercial member Jim Frerichs (who has a U320) 308-440-5154 and he had me do a series of tests to the thermostat which determined that it works perfectly.
When the blower motor failed (later in the same day I ordered the replacement) it blew the fuse in the furnace which caused it to disappear from the thermostat.
To reset the thermostat he told me to switch the thermostat Off the On, press the mode button, then hold the two lower buttons and push the mode button once with the bottom buttons still held, then release the lower buttons and the furnace will reappear.
He told me that he rebuilds the thermostats when they fail and the worst thing you can do is to quickly and repeatedly press the buttons if they are slow to respond because it "fry's" the chip under the button.
Good info. When my thermostat was acting up, I bought and replaced the buttons/contacts and it works like new.