diff --git a/pytec/tec_qt.py b/pytec/tec_qt.py
index be47a6c..7ac6560 100644
--- a/pytec/tec_qt.py
+++ b/pytec/tec_qt.py
@@ -123,7 +123,7 @@ class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
         if fan_settings is None:
             return
         with QSignalBlocker(self.fan_power_slider):
-            self.fan_power_slider.setValue(fan_settings["fan_pwm"])
+            self.fan_power_slider.setValue(fan_settings["fan_pwm"] or 100) # 0 = PWM off = full strength
             self.fan_power_slider.setEnabled(not fan_settings["auto_mode"])
         with QSignalBlocker(self.fan_auto_box):
             self.fan_auto_box.setChecked(fan_settings["auto_mode"])