F04
Westinghouse
Low flame signal / marginal flame sensing
Furnace shows F04; blower runs but burners do not light, or unit cycles off quickly.
Advertisements
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Advertisements
Possible Causes
Partially dirty flame sensor, Poor burner grounding, Low microamp flame current due to weak gas flame, Loose neutral connection to IFC
How to Fix / Troubleshooting
Safety: Turn off power and gas before cleaning components.
Steps:
- Clean the flame sensor thoroughly as described under E4.
- Inspect the burner rack mounting screws and ground strap from burner to furnace chassis; tighten if loose.
- Check the neutral (white) wire connection at the control board and junction box; tighten any loose wirenuts or screws.
- If you have a meter capable of measuring DC microamps in series with the flame sensor, verify that flame current meets Westinghouse specifications (often >1.0 µA). Low readings may indicate gas or burner issues requiring a technician.
Advertisements
Repair Difficulty
Medium
3/5
Advertisements