E9
Tuya Configuration or Hardware Protection Lockout

Thermostat displays E9 and refuses to start heating or cooling; often after a wiring change or power surge

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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

Incorrect system type configuration (heat pump vs boiler), Internal self-test failure on Tuya PCB, Relay driver fault, Firmware-detected unsafe state

How to Fix / Troubleshooting

Safety first: Turn off power before changing wiring or opening the thermostat.

Steps to troubleshoot:

  • Enter the installer or advanced settings menu (refer to Tuya thermostat manual) and verify system type (e.g., 1-stage heat, 2-pipe fan coil, heat pump) matches your HVAC system.
  • Restore factory defaults for installer settings if you are unsure what was changed.
  • Power-cycle the thermostat by turning off the breaker for 1–2 minutes, then turning it back on.
  • If E9 appeared after a wiring change, double-check all connections against the Tuya wiring diagram; correct any miswired terminals.
  • If the error persists and the thermostat will not exit lockout, the main board may have a hardware fault; replace the thermostat.
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Repair Difficulty

Medium 3/5

Required Part

Main Control PCB (Tuya Smart Thermostat)
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