A Honeywell thermostat screen going suddenly blank is typically caused by exhausted batteries, a tripped circuit breaker, or a blown low-voltage control fuse on your indoor HVAC equipment. If your Honeywell model uses backup batteries, replacing them often solves the problem instantly. If it is hardwired, a sudden power loss from a tripped breaker or a blown 3-amp or 5-amp fuse on the furnace control board will turn the screen dark. Power surges can also fry internal components. You can troubleshoot by removing the faceplate, checking for loose wires, replacing batteries, and inspecting the furnace fuse. You can verify that the issue is resolved when the display screen illuminates and reconnects to your HVAC system.
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