6 FLASHES
Ruud
Pressure Switch Cycle Lockout / Reversed Polarity or Ground Fault (varies by model)
The status LED shows 6 flashes; the furnace will not start the heating cycle, and the inducer may run briefly then stop.
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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.
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Possible Causes
Reversed line voltage polarity, furnace not properly grounded, pressure switch opening and closing too rapidly, or a loose neutral connection at the control board.
How to Fix / Troubleshooting
Safety: This involves line voltage. If you are not comfortable working with 120 VAC, contact a licensed electrician or HVAC technician.
Steps to check:
- Verify outlet polarity: If the furnace is cord-connected, use a plug-in outlet tester to confirm hot/neutral/ground connections are correct. For hard-wired units, an electrician should verify wiring at the disconnect and furnace junction box.
- Inspect ground connection: Ensure the green ground wire is securely attached to the furnace chassis and that the control board's ground lug is tight.
- Check neutral wiring: Confirm the neutral (white) wire is firmly connected at the furnace and not improperly shared with other circuits.
- Observe pressure switch behavior: If the code refers to pressure switch cycling, inspect venting, condensate drain, and inducer as described in the 3-FLASHES procedure. Rapid on/off of the switch can cause lockout.
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Repair Difficulty
Hard
4/5
Required Part
Integrated Furnace Control Board
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