diff --git a/esphome/components/thermostat/thermostat_climate.cpp b/esphome/components/thermostat/thermostat_climate.cpp
index d52a22f880d..eb3e756bc2a 100644
--- a/esphome/components/thermostat/thermostat_climate.cpp
+++ b/esphome/components/thermostat/thermostat_climate.cpp
@@ -606,6 +606,16 @@ void ThermostatClimate::switch_to_action_(climate::ClimateAction action, bool pu
 }
 
 void ThermostatClimate::switch_to_supplemental_action_(climate::ClimateAction action) {
+  // Always cancel max-runtime timers and clear exceeded flags when transitioning to idle/off,
+  // even if supplemental_action_ is already idle (early-return path). This prevents a stale
+  // heating_max_runtime_exceeded_ flag from triggering supplemental on the next heating cycle
+  // when HEATING_MAX_RUN_TIME fires while the main action is already IDLE.
+  if (action == climate::CLIMATE_ACTION_OFF || action == climate::CLIMATE_ACTION_IDLE) {
+    this->cancel_timer_(thermostat::THERMOSTAT_TIMER_COOLING_MAX_RUN_TIME);
+    this->cancel_timer_(thermostat::THERMOSTAT_TIMER_HEATING_MAX_RUN_TIME);
+    this->cooling_max_runtime_exceeded_ = false;
+    this->heating_max_runtime_exceeded_ = false;
+  }
   // setup_complete_ helps us ensure an action is called immediately after boot
   if ((action == this->supplemental_action_) && this->setup_complete_) {
     // already in target mode
@@ -975,8 +985,10 @@ void ThermostatClimate::cooling_on_timer_callback_() {
 void ThermostatClimate::fan_mode_timer_callback_() {
   ESP_LOGVV(TAG, "fan_mode timer expired");
   this->switch_to_fan_mode_(this->fan_mode.value_or(climate::CLIMATE_FAN_ON));
-  if (this->supports_fan_only_action_uses_fan_mode_timer_)
+  if (this->supports_fan_only_action_uses_fan_mode_timer_) {
     this->switch_to_action_(this->compute_action_());
+    this->switch_to_supplemental_action_(this->compute_supplemental_action_());
+  }
 }
 
 void ThermostatClimate::fanning_off_timer_callback_() {