American Standard Hard Lockout – Exceeded Retry Limit

Error code 20 and furnace will not start, LED indicates lockout due to too many retries

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.

Possible Causes

Unresolved ignition or flame sense issues, Persistent pressure switch faults, Repeated limit trips, Control board safety lockout on American Standard furnace

How to Fix / Troubleshooting

Safety: Identify and correct the underlying fault before resetting lockout.

Review prior error history:
- Many boards flash the last fault before lockout; note the pattern.
Correct root cause:
- Address ignition, pressure switch, or limit issues as indicated by previous codes.
Reset lockout:
- Turn off power for at least 30 seconds.
- Restore power and monitor a full heat cycle.
If lockout recurs, contact a qualified HVAC technician for full diagnostics.

Repair Difficulty

Professional Required 5/5