Google Nest Heat Call Signal Not Reaching Furnace

Nest thermostat calls for heat but furnace does not start

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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

Loose W1 wire at Nest base, Broken W1 conductor, Failed furnace control board heat relay, Open safety switch (limit, rollout, pressure switch)

How to Fix / Troubleshooting

Safety first: Turn off furnace power before opening panels or touching wiring.

  • Confirm Nest is calling for heat: Set the thermostat several degrees above room temperature and verify it indicates heating.
  • Inspect W1 wiring: Remove the Nest display and ensure the W1 wire is fully inserted. Check the same wire at the furnace W/W1 terminal.
  • Check furnace status lights: Many furnaces have diagnostic LEDs. After restoring power, observe any blink codes and refer to the furnace manual.
  • Reset safety switches: Ensure the furnace door switch is depressed by the panel. Check for manual reset rollout switches (only if you know their location and function).

If the furnace still does not start with a confirmed 24V call on W1, the control board or another internal furnace component may be faulty and should be serviced by a professional.

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Repair Difficulty

Hard 4/5

Required Part

Nest Thermostat Base (W1 terminal), Furnace Control Board
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