Why are 'Heat On' or 'Cool On' flashing on my thermostat screen?
The 'Heat On' or 'Cool On' messages flashing on the screen indicate that the compressor protection feature is engaged. This is a safety feature that prevents damage to the compressor. You should wait 5 minutes for the system to restart safely without damaging the compressor.
From the official Honeywell Set Temp RTH5160 Thermostat manual, page 14
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