Err 18
Burnham
Communication Fault with External Zone Panel
Boiler intermittently shows “Err 18” and may ignore some zone calls
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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
Loose low-voltage wiring between boiler and zone control, Incorrect priority wiring, Faulty zone control board, Control configuration mismatch
How to Fix / Troubleshooting
Safety first: Turn off power to both the boiler and any external zone control panels.
- Identify communication terminals: On Burnham boilers with integrated Sage controls, locate the terminals used for communication with external panels (e.g., “BUS”, “ZC/ZR”, or specific low-voltage terminals).
- Inspect wiring: Ensure all low-voltage wires are firmly attached, correctly landed, and not shorted between terminals.
- Check zone panel power: Verify the external zone control (Taco, Honeywell, etc.) has power and its LEDs indicate normal operation.
- Review configuration: Confirm that the boiler is set up for external zone control in the installer menu if required.
- Test with single zone: Temporarily connect a single thermostat directly to the boiler TT terminals to see if Err 18 disappears. If so, the issue is in the external panel or wiring.
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Repair Difficulty
Medium
3/5
Required Part
Zone Control Panel
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