H4
Fraser-Johnston
System Lockout / Multiple Faults Detected
H4 displayed, system stops and may not respond to thermostat
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
Repeated high/low pressure trips, Multiple sensor errors, Control board safety lockout, Incorrect wiring or configuration
How to Fix / Troubleshooting
Safety: Turn off power to both indoor and outdoor units.
- Record prior codes: If possible, access the Fraser‑Johnston control history to see which faults triggered H4.
- Correct underlying issues: Address any airflow, sensor, or pressure-related problems indicated by earlier codes.
- Reset lockout: Turn off power at breakers/disconnects for at least 10 minutes. Restore power and test operation.
- Check configuration: Verify dip switches or setup parameters on the control board match the installed system (tonnage, heat pump vs. AC only, etc.).
- Persistent H4: May indicate a failing control board that needs replacement.
Advertisements
Repair Difficulty
Hard
4/5
Required Part
System Control Board
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements