20 Most Recent Honeywell TH9421C1004 VisionPRO IAQ Total Home Comfort System Questions & Answers

Sounds like a all the bells and whistles thermostat, why did you chose that one? 090 Data interface is continuously busy. A log of error codes can be viewed at the end of the installer setup after the system tests. Active errors will be shown first. The Error Log will log the last ten errors (active and inactive). Pressing the reset button will clear all inactive errors from the error log; active errors can not be cleared until the condition has been remedially busy

We'd love to help resolve this. Please give us a call at 1.855.733.5465 and our customer support team will be happy to troubleshoot with you.

On Honeywell thermostats you have to program the thermostat on the setup mode to have the auto to be on the display. The setup instructions will walk up through it. If you do not have them, you can down load them to you computer.

Make sure there is 24 Volts between the R & Common wires connected to the thermostat subbase.

Pull the thermostat face off the wall. Wait a few minutes, & gently line up the pins and place back on. Let display pull up. If that doesn't work, your thermostat is probably under warranty...Replace.

check your float switch. On your air hander you have 3/4 white pvc coming out of bottom of unit, where the water drains out. If you have a float and your drain line is plugged it will make your tstat go blank. vacuum the drain line where it comes out of the ground outside.

That's very unlikely. I'd sooner believe the cat has been playing with it or it gets changed when someone wearing a backpack brushes past it (sometimes the straps or zipper pulls snag the oddest things). You can get a thermostat guard to prevent this if your landlord permits it.