diff --git a/klippy/extras/heaters.py b/klippy/extras/heaters.py
index 7cb663a4a279..1454354272d2 100644
--- a/klippy/extras/heaters.py
+++ b/klippy/extras/heaters.py
@@ -14,6 +14,7 @@
 MAX_HEAT_TIME = 5.0
 AMBIENT_TEMP = 25.
 PID_PARAM_BASE = 255.
+MAX_MAINTHREAD_TIME = 5.0
 
 class Heater:
     def __init__(self, config, sensor):
@@ -37,7 +38,7 @@ def __init__(self, config, sensor):
         self.max_power = config.getfloat('max_power', 1., above=0., maxval=1.)
         self.smooth_time = config.getfloat('smooth_time', 1., above=0.)
         self.inv_smooth_time = 1. / self.smooth_time
-        self.is_shutdown = False
+        self.verify_mainthread_time = -999.
         self.lock = threading.Lock()
         self.last_temp = self.smoothed_temp = self.target_temp = 0.
         self.last_temp_time = 0.
@@ -66,7 +67,7 @@ def __init__(self, config, sensor):
         self.printer.register_event_handler("klippy:shutdown",
                                             self._handle_shutdown)
     def set_pwm(self, read_time, value):
-        if self.target_temp <= 0. or self.is_shutdown:
+        if self.target_temp <= 0. or read_time > self.verify_mainthread_time:
             value = 0.
         if ((read_time < self.next_pwm_time or not self.last_pwm_value)
             and abs(value - self.last_pwm_value) < 0.05):
@@ -91,7 +92,7 @@ def temperature_callback(self, read_time, temp):
             self.can_extrude = (self.smoothed_temp >= self.min_extrude_temp)
         #logging.debug("temp: %.3f %f = %f", read_time, temp)
     def _handle_shutdown(self):
-        self.is_shutdown = True
+        self.verify_mainthread_time = -999.
     # External commands
     def get_name(self):
         return self.name
@@ -129,6 +130,9 @@ def alter_target(self, target_temp):
             target_temp = max(self.min_temp, min(self.max_temp, target_temp))
         self.target_temp = target_temp
     def stats(self, eventtime):
+        est_print_time = self.mcu_pwm.get_mcu().estimated_print_time(eventtime)
+        if not self.printer.is_shutdown():
+            self.verify_mainthread_time = est_print_time + MAX_MAINTHREAD_TIME
         with self.lock:
             target_temp = self.target_temp
             last_temp = self.last_temp