3
Low-heat pressure switch did not close or reopened
This code typically points to
- Proper vent sizing issue
- Air leak between vestibule/blower compartment
- Low inlet gas pressure if LGPS used
- Restricted vent
- Disconnected/obstructed tubing
- Defective/miswired switch
- Excessive wind
- Plugged condensate drain
- Water in vent
- Defective inducer
- Low inducer voltage
Next checks to confirm
- Run proving circuit live at low heat and work through OEM list above
Escalation
Escalate to inducer or vent system if switch and tubing check good.
Reset behavior
If open longer than 5 minutes inducer shuts off for 15 minutes before retry.
Urgent
Fix now