Thermostat shows E8 and screen is dim or flickering

Safety first: Turn off power at the breaker before removing the thermostat. Use a voltage tester to confirm power is off.

Steps to troubleshoot E8 (low voltage):

• 1. Inspect wiring connections:
  • Remove the thermostat from the backplate.
  • Check that the live (L) and neutral (N) wires are firmly secured in their terminals.
  • Tighten any loose screws and ensure no copper is exposed.
• 2. Measure supply voltage:
  • With power restored and using a multimeter, measure voltage between L and N at the thermostat.
  • For mains models, it should be close to 230V (EU) or 120V (US). For low‑voltage models, verify against the rated input (e.g., 24V AC).
  • If voltage is significantly low, the issue may be upstream in the electrical circuit.
• 3. Check shared circuits:
  • If the thermostat shares a circuit with heavy loads (heaters, motors), voltage sag may occur.
  • Consider moving the thermostat to a dedicated circuit or reducing load on the existing one.
• 4. Evaluate internal power supply:
  • If supply voltage is correct but E8 persists and the display flickers, the internal power supply components (e.g., capacitors) may be failing.
  • In this case, the thermostat should be replaced.

When to call a professional: Any work involving live mains measurements or circuit reconfiguration should be done by a licensed electrician.