diff --git a/src/NodeHeizung.h b/src/NodeHeizung.h
index 7d8840c..3ea35ad 100644
--- a/src/NodeHeizung.h
+++ b/src/NodeHeizung.h
@@ -9,6 +9,10 @@
 
 class NodeHeizung final : public Node {
 
+  const unsigned long MAX_AGE_SECONDS = 10;
+
+  const unsigned long OVERDUE_SECONDS = 60;
+
   DHT22 keller;
 
   Max6675Sensor abgas;
@@ -37,19 +41,19 @@ class NodeHeizung final : public Node {
 
 public:
 
-  NodeHeizung() : keller(13, "keller", 0.5, 2, 0.5, 60),
-                  abgas(27, 26, 25, "heizung/abgas", 2, 60),
+  NodeHeizung() : keller(13, "keller", 0.5, 2, 0.5, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  abgas(27, 26, 25, "heizung/abgas", 2, MAX_AGE_SECONDS, OVERDUE_SECONDS),
                   dallas(14),
-                  pufferVorlauf(dallas, 0xAA0121125E4A7528, "heizung/puffer/vorlauf", 1.0, 60),
-                  pufferRuecklauf(dallas, 0x3E0121126A163B28, "heizung/puffer/ruecklauf", 1.0, 60),
-                  pufferEingang(dallas, 0x0201211240EE3128, "heizung/puffer/eingang", 1.0, 60),
-                  pufferSpeicher(dallas, 0x1001211233D3A428, "heizung/puffer/speicher", 1.0, 60),
-                  pufferAusgang(dallas, 0xE80121126FFD9328, "heizung/puffer/ausgang", 1.0, 60),
-                  pufferZirkulation(dallas, 0x540121124A48FD28, "heizung/puffer/zirkulation", 1.0, 60),
-                  heizkreisVorlauf(dallas, 0x330121126F984728, "heizung/heizkreis/vorlauf", 1.0, 60),
-                  heizkreisRuecklauf(dallas, 0x4201211270337B28, "heizung/heizkreis/ruecklauf", 1.0, 60),
-                  abwasser(dallas, 0x810121126EE53828, "abwasser", 1.0, 60),
-                  reserve(dallas, 0x0D0121126716CF28, "__RESERVE__", 1.0, 60) {
+                  pufferVorlauf(dallas, 0xAA0121125E4A7528, "heizung/puffer/vorlauf", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  pufferRuecklauf(dallas, 0x3E0121126A163B28, "heizung/puffer/ruecklauf", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  pufferEingang(dallas, 0x0201211240EE3128, "heizung/puffer/eingang", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  pufferSpeicher(dallas, 0x1001211233D3A428, "heizung/puffer/speicher", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  pufferAusgang(dallas, 0xE80121126FFD9328, "heizung/puffer/ausgang", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  pufferZirkulation(dallas, 0x540121124A48FD28, "heizung/puffer/zirkulation", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  heizkreisVorlauf(dallas, 0x330121126F984728, "heizung/heizkreis/vorlauf", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  heizkreisRuecklauf(dallas, 0x4201211270337B28, "heizung/heizkreis/ruecklauf", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  abwasser(dallas, 0x810121126EE53828, "abwasser", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+                  reserve(dallas, 0x0D0121126716CF28, "__RESERVE__", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS) {
     //
   };
 
diff --git a/src/NodeTest.h b/src/NodeTest.h
index d379a66..75795ec 100644
--- a/src/NodeTest.h
+++ b/src/NodeTest.h
@@ -10,6 +10,10 @@
 
 class NodeTest final : public Node {
 
+  const unsigned long MAX_AGE_SECONDS = 10;
+
+  const unsigned long OVERDUE_SECONDS = 60;
+
   Dallas dallas;
 
   DallasSensor test;
@@ -19,8 +23,8 @@ class NodeTest final : public Node {
 public:
 
   NodeTest() : dallas(27),
-               test(dallas, 0xC90417C1C5C0FF28, "test/ds18b20", 1.0, 60),
-               testraum(26, "test/dht22", 0.5, 2, 1, 605) {
+               test(dallas, 0xC90417C1C5C0FF28, "test/ds18b20", 1.0, MAX_AGE_SECONDS, OVERDUE_SECONDS),
+               testraum(26, "test/dht22", 0.5, 2, 1, MAX_AGE_SECONDS, OVERDUE_SECONDS) {
     //
   };
 
diff --git a/src/patrix/sensor/DHT22.h b/src/patrix/sensor/DHT22.h
index 71862e5..567cf78 100644
--- a/src/patrix/sensor/DHT22.h
+++ b/src/patrix/sensor/DHT22.h
@@ -22,12 +22,13 @@ public:
         const double temperatureThreshold,
         const double humidityRelativeThreshold,
         const double humidityAbsoluteThreshold,
-        const unsigned long dueSeconds
+        const unsigned long maxAgeSeconds,
+        const unsigned long overdueSeconds
   ) : Sensor(name),
       sensor(pin, DHT_TYPE_22),
-      temperature("temperature", temperatureThreshold, dueSeconds),
-      humidityRelative("humidityRelative", humidityRelativeThreshold, dueSeconds),
-      humidityAbsolute("humidityAbsolute", humidityAbsoluteThreshold, dueSeconds) {
+      temperature(name, "temperature", temperatureThreshold, maxAgeSeconds, overdueSeconds),
+      humidityRelative(name, "humidityRelative", humidityRelativeThreshold, maxAgeSeconds, overdueSeconds),
+      humidityAbsolute(name, "humidityAbsolute", humidityAbsoluteThreshold, maxAgeSeconds, overdueSeconds) {
     //
   }
 
@@ -48,7 +49,7 @@ public:
     json[name][humidityAbsolute.getName()] = humidityAbsolute.getCurrentValue();
   }
 
-  bool isDue() const override {
+  bool isDue() override {
     return temperature.isDue() || humidityRelative.isDue() || humidityAbsolute.isDue();
   }
 
diff --git a/src/patrix/sensor/Dallas.h b/src/patrix/sensor/Dallas.h
index 869f3bd..766a0d9 100644
--- a/src/patrix/sensor/Dallas.h
+++ b/src/patrix/sensor/Dallas.h
@@ -5,7 +5,7 @@
 #include "OneWire.h"
 #include "DallasTemperature.h"
 
-#define DALLAS_TIMEOUT_MILLISECONDS   3000
+#define DALLAS_INTERVAL_MILLISECONDS    2000
 
 class Dallas {
 
@@ -29,7 +29,7 @@ public:
   }
 
   void loop() {
-    if (lastMillis == 0 || millis() - lastMillis > DALLAS_TIMEOUT_MILLISECONDS) {
+    if (lastMillis == 0 || millis() - lastMillis > DALLAS_INTERVAL_MILLISECONDS) {
       if (converting) {
         error("Dallas timeout!");
       }
diff --git a/src/patrix/sensor/DallasSensor.h b/src/patrix/sensor/DallasSensor.h
index d0fc9cd..11d5149 100644
--- a/src/patrix/sensor/DallasSensor.h
+++ b/src/patrix/sensor/DallasSensor.h
@@ -21,11 +21,12 @@ public:
     const uint64_t address,
     const char *name,
     const double threshold,
-    const unsigned long dueSeconds
+    const unsigned long maxAgeSeconds,
+    const unsigned long overdueSeconds
   ) : Sensor(name),
       sensors(sensors),
       address(address),
-      temperature("temperature", threshold, dueSeconds) {
+      temperature(name, "temperature", threshold, maxAgeSeconds, overdueSeconds) {
     //
   }
 
@@ -40,7 +41,7 @@ public:
     json[name][temperature.getName()] = temperature.getCurrentValue();
   }
 
-  bool isDue() const override {
+  bool isDue() override {
     return temperature.isDue();
   }
 
diff --git a/src/patrix/sensor/Max6675Sensor.h b/src/patrix/sensor/Max6675Sensor.h
index 9fe7628..cb0c079 100644
--- a/src/patrix/sensor/Max6675Sensor.h
+++ b/src/patrix/sensor/Max6675Sensor.h
@@ -22,10 +22,11 @@ public:
     const int8_t pinCLK,
     const char *name,
     const double threshold,
-    const unsigned long dueSeconds
+    const unsigned long maxAgeSeconds,
+    const unsigned long overdueSeconds
   ) : Sensor(name),
       sensor(pinCLK, pinCS, pinMISO),
-      temperature("temperature", threshold, dueSeconds) {
+      temperature(name, "temperature", threshold, maxAgeSeconds, overdueSeconds) {
     //
   }
 
@@ -39,7 +40,7 @@ public:
     json[name][temperature.getName()] = temperature.getCurrentValue();
   }
 
-  bool isDue() const override {
+  bool isDue() override {
     return temperature.isDue();
   }
 
diff --git a/src/patrix/sensor/Sensor.h b/src/patrix/sensor/Sensor.h
index 0cd5010..b04e20b 100644
--- a/src/patrix/sensor/Sensor.h
+++ b/src/patrix/sensor/Sensor.h
@@ -21,7 +21,7 @@ public:
 
   virtual void toJson(JsonDocument& json) = 0;
 
-  virtual bool isDue() const = 0;
+  virtual bool isDue() = 0;
 
   virtual void markSent() = 0;
 
diff --git a/src/patrix/sensor/Value.h b/src/patrix/sensor/Value.h
index 096e914..f164a10 100644
--- a/src/patrix/sensor/Value.h
+++ b/src/patrix/sensor/Value.h
@@ -1,49 +1,62 @@
 #ifndef VALUE_H
 #define VALUE_H
+#include <patrix/log.h>
 
 class Value {
 
+  const char *parent;
+
   const char *name;
 
   double threshold;
 
-  unsigned long dueSeconds;
+  unsigned long maxAgeMillis;
+
+  unsigned long overdueSeconds;
 
   double currentValue = NAN;
 
-  unsigned long currentInterval = 0;
+  unsigned long currentMillis = 0;
 
   double sentValue = NAN;
 
-  unsigned long sentInterval = 0;
+  time_t sentInterval = 0;
 
 public:
 
   Value(
+    const char *parent,
     const char *name,
     const double threshold,
-    const unsigned long dueSeconds
-  ) : name(name),
+    const unsigned long maxAgeSeconds,
+    const unsigned long overdueSeconds
+  ) : parent(parent),
+      name(name),
       threshold(threshold),
-      dueSeconds(dueSeconds) {
+      maxAgeMillis(maxAgeSeconds * 1000),
+      overdueSeconds(overdueSeconds) {
     //
   }
 
   void update(const double value) {
     currentValue = value;
-    currentInterval = time(nullptr) / dueSeconds;
+    currentMillis = millis();
   }
 
-  bool isDue() const {
+  bool isDue() {
+    if (!isnan(currentValue) && millis() - currentMillis > maxAgeMillis) {
+      warn("Value too old: %s/%s", parent, name);
+      update(NAN);
+    }
     const auto dueToNAN = isnan(currentValue) != isnan(sentValue);
     const auto dueToThreshold = abs(sentValue - currentValue) >= threshold;
-    const auto dueToTime = currentInterval != sentInterval;
+    const auto dueToTime = sentInterval != time(nullptr) / overdueSeconds;
     return dueToNAN || dueToThreshold || dueToTime;
   }
 
   void markSent() {
     sentValue = currentValue;
-    sentInterval = currentInterval;
+    sentInterval = time(nullptr) / overdueSeconds;
   }
 
   const char *getName() const {