diff -r 7ed5c380e21b -r f52b18a2a4d1 www/js/mon_fermenter.js
--- a/www/js/mon_fermenter.js	Tue May 19 15:09:31 2020 +0200
+++ b/www/js/mon_fermenter.js	Tue May 19 22:47:35 2020 +0200
@@ -363,21 +363,27 @@
     $('#gaugeContainer_air').jqxGauge(range);
     $('#gaugeContainer_beer').jqxGauge(range);
 
-    $('#gaugeContainer_air').jqxGauge({ caption: { value: 'Lucht: ' + record.air_temperature.toFixed(3) }});
-    $('#gaugeContainer_air').jqxGauge({ value: record.air_temperature });
+    if (record.air_temperature !== undefined) {
+     $('#gaugeContainer_air').jqxGauge({ caption: { value: 'Lucht: ' + record.air_temperature.toFixed(3) }});
+     $('#gaugeContainer_air').jqxGauge({ value: record.air_temperature });
+    }
     if (record.air_state == 'OK') {
      $('#gaugeContainer_air').jqxGauge({ disabled: false });
     } else {
      $('#gaugeContainer_air').jqxGauge({ disabled: true });
     }
-    $('#gaugeContainer_beer').jqxGauge({ caption: { value: 'Bier: ' + record.beer_temperature.toFixed(3) }});
-    $('#gaugeContainer_beer').jqxGauge({ value: record.beer_temperature });
+    if (record.beer_temperature !== undefined) {
+     $('#gaugeContainer_beer').jqxGauge({ caption: { value: 'Bier: ' + record.beer_temperature.toFixed(3) }});
+     $('#gaugeContainer_beer').jqxGauge({ value: record.beer_temperature });
+    }
     if (record.beer_state == 'OK') {
      $('#gaugeContainer_beer').jqxGauge({ disabled: false });
     } else {
      $('#gaugeContainer_beer').jqxGauge({ disabled: true });
     }
-    $('#gaugeContainer_chiller').jqxGauge({ value: record.chiller_temperature });
+    if (record.chiller_temperature !== undefined) {
+     $('#gaugeContainer_chiller').jqxGauge({ value: record.chiller_temperature });
+    }
     if (record.chiller_state == 'OK') {
      $('#gaugeContainer_chiller').jqxGauge({ disabled: false });
     } else {
@@ -620,8 +626,11 @@
     record.beer_temperature = obj.beer_temperature;
     record.chiller_state = obj.chiller_state;
     record.chiller_temperature = obj.chiller_temperature;
-    record.heater_state = obj.heater_state;
-    record.cooler_state = obj.cooler_state;
+    if (obj.heater_state !== undefined)
+     record.heater_state = obj.heater_state;
+    if (obj.cooler_state !== undefined)
+     record.cooler_state = obj.cooler_state;
+    if (obj.fan_state !== undefined)
     record.fan_state = obj.fan_state;
     if (obj.door_address)
      record.door_state = obj.door_state;