E1 error and thermostat shows very low or negative room temperature values.

Safety: No internal wiring work is required for this procedure.

• Step 1 – Compare with reference thermometer:
  • Place a reliable thermometer near the thermostat.
  • Wait 15–20 minutes and compare readings.
• Step 2 – Adjust calibration:
  • Enter installer menu and locate Temperature Offset or Calibration.
  • Adjust the offset so the displayed temperature matches the reference.
• Step 3 – Reset calibration if extreme:
  • If offset is set to an extreme value, reset to 0°C and re-test.
• Step 4 – Firmware update:
  • Update firmware if an update addresses sensor accuracy issues.
• Step 5 – Replace thermostat if sensor is unstable:
  • If readings fluctuate wildly or E1 persists, the internal sensor may be defective.
  • Replace the Protherm smart thermostat.