Thermostat calls for heat but furnace does nothing (no sound, no lights) even though power is present

Safety: Turn off power before handling low-voltage wiring.

• 1. Check fuse: Inspect and replace the low-voltage fuse on the control board if blown.
• 2. Thermostat test: Temporarily jumper R to W at the furnace control board. If the furnace starts, the thermostat or its wiring is faulty.
• 3. Replace thermostat batteries: If applicable, replace and reprogram the thermostat.
• 4. Professional help: If there is no 24V between R and C, the transformer or control board may be failed and should be replaced by a technician.