The thermostat has power but will not turn on heating when the temperature is set higher than the room temperature.

Safety: Turn OFF power to the indoor unit before accessing the control board or thermostat wiring.

• Verify mode and setpoint: Ensure the thermostat is in HEAT mode and the setpoint is several degrees above the displayed room temperature.
• Check W/W1 wiring: Remove the thermostat and confirm the W or W1 terminal has a wire securely attached. At the Ruud indoor control board, verify the same wire is on the W/W1 terminal.
• Fuse inspection: Inspect the low-voltage fuse on the indoor control board and replace if blown. If it blows again when calling for heat, there is a short in the heat circuit.
• Bypass test (advanced): With power ON and the blower door switch held closed, briefly jumper R to W/W1 at the indoor control board. If the furnace or air handler starts heating, the problem is upstream (thermostat or wiring). Remove the jumper immediately after the test.
• Thermostat replacement: If wiring and the fuse are good and the system responds to an R–W jumper but not to the thermostat, the thermostat's heat output has likely failed. Replace the thermostat.