Fault Code Lookup

HVAC Sales Master

Open Temperature Limit Circuit

This code typically points to

Open temperature limit circuit
Burner-box manual-reset limit tripped
Vent/combustion-air blockage

Next checks to confirm

Check limit continuity
Inspect burner-box manual-reset limit
Check vent and combustion-air terminations for blockage

Escalation

Gas shutoff / heating interrupted

Reset behavior

Burner-box manual-reset limit can be reset after blockage cleared; otherwise qualified servicer reset.

Safety Critical

Immediate concern

⚠ Cross-generation conflict

Legacy Code 4 was 'open limit'. The newer S-series e04 includes rollout and reverse-airflow switches in the same code — diagnostic path must branch on which device opened.

Source

Trane 18-CD19D5-21 Installer's Guide, p.35-37

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