E6
Tuya Power Supply or Low-Voltage Input Fault

Thermostat shows E6 and cannot control the HVAC system; often on Tuya Wi-Fi thermostats for boilers or heat pumps

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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 supply voltage (e.g., 24V AC missing), Loose power terminal connection, Blown internal fuse on Tuya thermostat, Faulty internal SMPS power module

How to Fix / Troubleshooting

Safety first: Turn off power at the HVAC service switch or main breaker before touching any wiring.

Steps to troubleshoot:

  • Confirm the thermostat is wired according to the Tuya wiring diagram (check line/neutral or 24V R/C connections).
  • Use a multimeter to measure voltage at the thermostat power terminals: for mains-powered models, verify 100–240V AC; for low-voltage models, verify 24V AC between R and C.
  • Tighten any loose terminal screws and ensure no copper is exposed that could short to adjacent terminals.
  • If correct voltage is present but E6 remains, remove the thermostat from the base and inspect for a small internal fuse; if blown, replace with the exact same rating if user-serviceable.
  • If there is no accessible fuse or a new fuse blows immediately, the internal power supply is likely defective; replace the thermostat.

Warning: Working on mains voltage can be hazardous. If you are not experienced, hire a qualified electrician or HVAC technician.

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Repair Difficulty

Hard 4/5

Required Part

Internal Power Supply Module / Fuse on Tuya Thermostat
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