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Troubleshooting code

Back to all DHC036HW*(L,M,H,X,Y,Z)B error codes

Trane DHC036HW*(L,M,H,X,Y,Z)B Ignition 4 Flash troubleshooting

High-temperature limit circuit open. Use this page to document the issue and prepare for service. GreenFlow should handle diagnosis for electrical, refrigerant, lockout, or recurring conditions.

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What the code means

Ignition 4 Flash: High-temperature limit circuit open

The Trane Precedent gas heat fault-code table identifies 4 flash as TCO-1 or TCO-2 high-temperature-limit circuit open, with wiring, airflow, filter, indoor blower, switch, or board issues listed as possible causes.

System area
Precedent gas heat ignition board
Service level
Call GreenFlow

Safe checks before calling

  • Confirm the thermostat is on, set correctly, and calling for heating or cooling.
  • Check the air filter and visible return-air path for obvious airflow restrictions.
  • Look around the outdoor unit for leaves, snow, ice, or other visible obstructions without opening the cabinet.
  • Take photos of the thermostat, outdoor unit, nameplate, and any visible flash pattern before scheduling service.

When to stop and call GreenFlow

Call GreenFlow if the code repeats, the system is locked out, heating or cooling is not restored, there is ice buildup, electrical odor, unusual noise, or any issue involving pressure switches, sensors, wiring, refrigerant, reversing-valve operation, or warranty coverage.

Share the visible code, model and serial number if available, photos, current symptoms, and whether the issue affects heating, cooling, or both.

Ignition 4 Flash questions

What does Ignition 4 Flash mean on a Trane DHC036HW*(L,M,H,X,Y,Z)B?

The Trane Precedent gas heat fault-code table identifies 4 flash as TCO-1 or TCO-2 high-temperature-limit circuit open, with wiring, airflow, filter, indoor blower, switch, or board issues listed as possible causes.

What should I safely check before scheduling service?

Check thermostat status, filter condition, visible outdoor-unit obstructions, and take photos of the flash pattern and nameplate. Do not open electrical panels or refrigerant-side components.

When should GreenFlow handle this code?

Call GreenFlow if the code repeats, the system is locked out, heating or cooling is not restored, there is ice buildup, electrical odor, unusual noise, or any issue involving pressure switches, sensors, wiring, refrigerant, reversing-valve operation, or warranty coverage.

Need help with this code?

GreenFlow can review the code, photos, equipment access, and symptoms before scheduling the right next step.

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