Thermostat displays E03 and shows room temperature as "--"; heating does not regulate correctly

Safety: Turn off power to the thermostat circuit (low-voltage from boiler or 230 V supply, depending on model) before opening the housing.

• Step 1 – Reboot: Remove power to the thermostat for 1–2 minutes, then restore. Check if E03 clears.
• Step 2 – Inspect location: Ensure the thermostat is not installed above a radiator, in direct sunlight, or in a damp area. Excess heat or moisture can damage the internal NTC sensor.
• Step 3 – Open housing: Carefully remove the thermostat front cover. Look for condensation, corrosion, or visible damage around the small NTC sensor (usually a bead or small component near air vents).
• Step 4 – Dry and clean: If moisture is present, gently dry the PCB with a soft cloth and allow it to air dry completely. Do not use a hair dryer or heat gun.
• Step 5 – Sensor test/replacement: A technician can measure the NTC resistance at room temperature and compare it to Immergas specifications. If out of range, the NTC or entire PCB must be replaced.
• Step 6 – Replace thermostat: If the sensor is integrated and not serviceable, replace the thermostat with a compatible Immergas smart thermostat.