A thermostat display screen going completely black or blank can be triggered by several electrical and battery-related failures. If your thermostat relies on removable alkaline batteries, a black or faded screen is almost always caused by dead batteries that have lost their charge over time. If your thermostat is hardwired without backup batteries, a black screen indicates a complete loss of 24-volt power from your indoor HVAC unit, which is commonly caused by a blown low-voltage fuse on the furnace control board, a tripped circuit breaker, or a loose transformer wire. Additionally, internal electronic component failure caused by power surges or extreme temperature fluctuations can permanently darken the liquid crystal display. You can troubleshoot by changing batteries and checking fuses. You can verify resolution when the screen turns on.
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