Thermostat display shows E01 and heating does not switch on

Safety first: Isolate power to the thermostat at the fused spur or consumer unit before removing the thermostat from the wall.

Steps to check and fix:

• Remove the thermostat from its wall plate (usually by loosening a small retaining screw at the bottom and gently pulling forward).
• Locate the floor sensor terminals (commonly marked as "S1/S2" or "NTC"). Ensure both wires are firmly clamped and not broken.
• Inspect the floor sensor cable where it enters the back box. Look for crushed, cut, or pulled-out cable.
• With power still isolated, use a multimeter set to resistance (Ω) and measure across the two sensor wires. A typical Heatmiser 10k NTC sensor should read around 8–15 kΩ at room temperature. If the meter shows OL (open circuit) or extremely high resistance, the sensor or cable is open.
• If the sensor is open circuit, replace it with a compatible Heatmiser 10k NTC floor sensor. Feed the new sensor into the floor conduit if available; if not possible, switch the thermostat to air sensor only mode (if supported) as a temporary workaround.
• Re-terminate the sensor wires securely, refit the thermostat, restore power, and confirm the E01 code has cleared.

When to call a professional: If the sensor is embedded in the floor without conduit and cannot be replaced without lifting tiles or screed, consult a heating installer or electrician.