Fault Code Lookup

HVAC Sales Master

Open Temperature Limit Switch

This code typically points to

Open temperature limit switch
Burner-box limit involvement
Vent/air termination blockage

Next checks to confirm

Check limit continuity
Inspect burner-box limit and vent/air terminations

Escalation

Heating interrupted / gas off

Reset behavior

Burner-box limit may be manually reset after blockage cleared.

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-CD20D3-21 Installer's Guide, p.35-36

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