3 Flashes
Low-pressure switch stuck open, or manual ON/OFF switch in OFF position, or auxiliary limit open on upflow-only applications
This code typically points to
- Switch not closing
- Gas valve switch off
- Aux limit open on upflow
- Vent restriction / inducer or tubing problems
Next checks to confirm
- Confirm gas-valve ON/OFF position
- Verify aux limit continuity where applicable
- Verify low-pressure switch closes during inducer run
Escalation
Escalate to inducer/venting/switch testing if switch still open under correct draft.
Reset behavior
Retry after condition is corrected.
Urgent
Fix now