The status LED flashes green once, repeatedly; the furnace does not start the heating cycle.

Steps to check:

• Confirm thermostat call: Set the thermostat to HEAT and raise the setpoint. Listen for a click at the thermostat. If none, the thermostat may be faulty.
• Measure 24 VAC: At the control board, measure between R and C. You should see approximately 24 VAC. If low or zero, check the furnace transformer and primary power.
• Check R and W continuity: With power off, check resistance between R and W at the furnace with the thermostat calling for heat. A closed circuit should read near 0 ohms. An open reading indicates a break in the thermostat or wiring.

Replace the thermostat or repair wiring as needed. If transformer output is low, replace the transformer with a Coleman-compatible 24 VAC unit.