Thermostat display shows E1 and will not control heating; set temperature changes have no effect.

Safety first: Turn off power to the heating system and thermostat at the boiler/isolation switch and the consumer unit (breaker) before opening any device.

Steps to check:

• Power-cycle the thermostat: Remove the thermostat from its wall plate (for models like Salus RT510RF, RT520RF, VS20WRF) or remove batteries for 2–3 minutes, then refit and test. If E1 clears temporarily and returns, the sensor is likely failing.
• Inspect the thermostat location: Ensure the thermostat is not installed above a radiator, in direct sunlight, or near a draught. Extreme temperatures can trigger sensor error on some Salus models.
• Check for moisture ingress: Remove the thermostat front cover and look for condensation, corrosion, or water marks around the sensor area (usually a small bead-like component near the air vents). If moisture is present, allow the unit to dry completely in a warm, dry place for several hours, then retest.
• Visual inspection of the sensor: With power off, inspect the NTC sensor on the PCB for cracks, burn marks, or broken leads. If the sensor is physically damaged, the thermostat head usually needs replacement as the sensor is board-mounted.
• Measure sensor resistance (advanced): If you have a multimeter and are competent, measure resistance across the NTC sensor pads. Compare to Salus service data (typically ~10kΩ at 25°C for many models). An open circuit (infinite) or near 0Ω indicates a failed sensor.

When to replace: If E1 persists after power-cycling and the sensor appears damaged or out of specification, replace the thermostat head or complete thermostat unit. Do not attempt PCB-level repair unless you are qualified.