American Standard Open Heat Call Circuit or Furnace Control Board Issue

Thermostat calls for heat but furnace does not start; display shows normal operation, no code

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Broken W wire between thermostat and furnace, Loose connection at furnace control board W terminal, Failed furnace control board heat input, Safety limit or pressure switch open

How to Fix / Troubleshooting

Safety: Turn off power to the furnace before removing access panels.

  • Confirm call for heat: On the thermostat, verify that it indicates a heating call (often a flame icon or status message).
  • Check W terminal at furnace: With power on and a call for heat, measure voltage between W and C at the furnace board. You should see 24V. If not, the wire or thermostat is suspect.
  • Inspect wiring: Tighten the W connection at the furnace board and look for breaks or splices in the thermostat cable.
  • Check furnace status LEDs: Many American Standard furnaces have diagnostic LEDs on the control board. Note any blink codes and refer to the furnace manual.

Note: If the board is receiving 24V on W but the furnace does not start, a technician should diagnose internal safeties and the control board.

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Repair Difficulty

Hard 4/5

Required Part

American Standard furnace control board or W call wiring
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