Thermostat display is completely blank and unresponsive; HVAC system does not run.

Safety first: Before opening any panels, turn off the main HVAC breakers. Use caution around live electrical components.

• Check breakers and switches: Verify that the furnace/air handler and outdoor unit breakers are ON and that any service switch near the indoor unit is not off.
• Inspect furnace control fuse: Remove the blower door and locate the low‑voltage blade fuse on the Payne control board. Replace only with the same amperage if blown, and watch for a repeat blow indicating a short.
• Verify R and C at thermostat: Remove the thermostat and check that the R and C wires are firmly attached and not broken. Tug gently to ensure they are secure.
• Measure 24VAC (advanced): With power on and a multimeter set to AC volts, measure between R and C at the furnace control board. If no voltage is present, the transformer may be failed and should be replaced by a technician.
• Replace thermostat if powered but dead: If 24VAC is present at the thermostat terminals but the display remains blank, the Payne smart thermostat is likely defective and should be replaced.