Thermostat shows E2 and cannot correctly regulate room temperature; display may show dashes instead of temperature.

Safety first: Switch off power to the thermostat at the breaker before touching any wiring.

Steps:

• Verify sensor connection: Remove the thermostat from the wall plate and check that the external sensor wires are firmly clamped in the correct terminals as per the Danfoss Ally wiring diagram.
• Inspect cable: Look for cuts, crushed sections, or signs of moisture in the sensor cable, especially where it enters the wall or floor.
• Check resistance: Using a multimeter, measure resistance across the sensor leads (with power off). Compare the reading to the Danfoss NTC sensor resistance table at room temperature (typically ~10kΩ at 25°C for many Danfoss sensors). If reading is near 0Ω (short) or infinite (open), the sensor is faulty.
• Reconnect or replace: Reseat the wires and tighten the terminals. If the sensor is defective, replace it with a Danfoss‑approved NTC floor/remote sensor of the correct value.
• Reset thermostat: Restore power and clear the error by rebooting or performing a factory reset if required by the manual.