Thermostat has power but will not turn on heating when room is below setpoint

Warning: Turn off power to the furnace before handling wiring.

• Step 1 – Verify settings:
  • Ensure the thermostat is set to Heat mode and the setpoint is above room temperature.
  • Check that system type is correctly set (conventional vs heat pump).
• Step 2 – Inspect W wiring:
  • Confirm the W/W1 wire is securely connected at both thermostat and furnace board.
• Step 3 – Test furnace response:
  • At the furnace board, jumper R to W; if the furnace starts heating, the issue is likely the thermostat or its wiring.
• Step 4 – Measure W output:
  • With a heat call active, measure voltage between W and C at the thermostat; should be ~24VAC.
  • If no voltage, the thermostat’s heat relay is likely defective.
• Step 5 – Replace thermostat if W output is bad:
  • Replace the thermostat if it cannot provide 24VAC on W with a heat call.