Johnson Controls
Heat Call Not Reaching Burner/Heat Source
Thermostat calls for heat, but only the fan runs and no warm air is produced.
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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
Miswired W/W1 terminal, Open high‑limit or rollout switch in furnace, Failed furnace control board heat relay, Thermostat configured for heat pump when system is conventional
How to Fix / Troubleshooting
Safety: Turn off power to the furnace and thermostat before opening panels. Gas and combustion components should be serviced by a qualified technician.
- Step 1 – Verify configuration: Confirm in the installer menu that the system type matches your equipment (conventional gas/oil vs. heat pump).
- Step 2 – Check thermostat wiring: Ensure the heating call wire is on W/W1 at both the thermostat and furnace control board.
- Step 3 – Observe furnace: With a call for heat, watch the furnace sequence (ignition, flame, blower). If the blower runs but no ignition occurs, the issue is in the furnace, not the thermostat.
- Step 4 – Safety switches: A tripped high‑limit or rollout switch can prevent burner operation. These should be tested and reset only by a qualified technician.
- Step 5 – Technician service: If wiring and configuration are correct, have a technician diagnose the furnace control board, gas valve, and safety circuits.
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Repair Difficulty
Professional Required
5/5
Required Part
Furnace Control Board / Heating Circuit (not thermostat)
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