Use WATCH_TEMP_INCREASE + TEMP_HYSTERESIS + 1 as difference limit

Marlin/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/configurator/config/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/Felix/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/Hephestos/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/K8200/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/SCARA/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/WITBOX/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/delta/biv2.5/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/delta/generic/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/delta/kossel_mini/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/makibox/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/example_configurations/tvrrug/Round2/Configuration_adv.h

@@ -25,7 +25,7 @@
    * Whenever an M104 or M109 increases the target temperature the firmware will wait for the
    * WATCH_TEMP_PERIOD to transpire, and if the temperature hasn't increased by WATCH_TEMP_INCREASE
    * degrees, the machine is halted, requiring a hard reset. This test restarts with any M104/M109,
-   * but only if the current temperature is below the target by at least 2 * WATCH_TEMP_INCREASE degrees.
+   * but only if the current temperature is far enough below the target for a reliable test.
    */
   #define WATCH_TEMP_PERIOD 16                // Seconds
   #define WATCH_TEMP_INCREASE 4               // Degrees Celsius

Marlin/temperature.cpp

@@ -1007,7 +1007,7 @@ void tp_init() {
    */
   void start_watching_heater(int e) {
     millis_t ms = millis() + WATCH_TEMP_PERIOD * 1000;
-    if (degHotend(e) < degTargetHotend(e) - (WATCH_TEMP_INCREASE * 2)) {
+    if (degHotend(e) < degTargetHotend(e) - (WATCH_TEMP_INCREASE + TEMP_HYSTERESIS + 1)) {
       watch_target_temp[e] = degHotend(e) + WATCH_TEMP_INCREASE;
       watch_heater_next_ms[e] = ms;
     }