E1
Tempstar
Indoor Unit Communication Error
Tempstar communicating thermostat shows E1; furnace may not respond or may run in backup mode.
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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
Open or shorted communication bus to furnace, Incorrect dip switch addressing on Tempstar indoor unit, Defective indoor control board, Reversed communication wires
How to Fix / Troubleshooting
Safety: Turn off power before adjusting dip switches or wiring.
- Step 1 – Verify wiring: Confirm that the communication wires are landed on the correct terminals at both thermostat and furnace, with no shorts between conductors.
- Step 2 – Check addressing: Some Tempstar communicating systems require proper dip switch settings for indoor unit type. Refer to the installation manual and adjust as needed.
- Step 3 – Inspect cable: Look for damage where the cable enters the furnace cabinet. Replace if insulation is cut or chewed.
- Step 4 – Reset system: Power down the system for 1–2 minutes, then restore and allow the thermostat to re-scan for equipment.
- Step 5 – Replace indoor board if needed: If communication still fails, the Tempstar indoor control board may be defective and require replacement.
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Repair Difficulty
Hard
4/5
Required Part
Tempstar Furnace Control Board
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