diff --git a/klippy/extras/heater_fan.py b/klippy/extras/heater_fan.py
index d69a7cf48..1294b4d24 100644
--- a/klippy/extras/heater_fan.py
+++ b/klippy/extras/heater_fan.py
@@ -17,22 +17,27 @@ class PrinterHeaterFan:
         self.heaters = []
         self.fan = fan.Fan(config, default_shutdown_speed=1.)
         self.fan_speed = config.getfloat("fan_speed", 1., minval=0., maxval=1.)
+        self.last_speed = 0.
     def handle_ready(self):
         pheaters = self.printer.lookup_object('heaters')
         self.heaters = [pheaters.lookup_heater(n.strip())
                         for n in self.heater_name.split(',')]
         reactor = self.printer.get_reactor()
-        reactor.register_timer(self.callback, reactor.NOW)
+        reactor.register_timer(self.callback, reactor.monotonic()+PIN_MIN_TIME)
     def get_status(self, eventtime):
         return self.fan.get_status(eventtime)
     def callback(self, eventtime):
-        power = 0.
+        speed = 0.
         for heater in self.heaters:
             current_temp, target_temp = heater.get_temp(eventtime)
             if target_temp or current_temp > self.heater_temp:
-                power = self.fan_speed
-        print_time = self.fan.get_mcu().estimated_print_time(eventtime)
-        self.fan.set_speed(print_time + PIN_MIN_TIME, power)
+                speed = self.fan_speed
+        if speed == self.last_speed:
+            return
+        self.last_speed = speed
+        curtime = self.printer.get_reactor().monotonic()
+        print_time = self.fan.get_mcu().estimated_print_time(curtime)
+        self.fan.set_speed(print_time + PIN_MIN_TIME, speed)
         return eventtime + 1.
 
 def load_config_prefix(config):